builtin/worktree.c, t/t2400-worktree-add.sh

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 654d27c3e1..46bc305116 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -116,6 +116,16 @@ static const char * const git_worktree_unlock_usage[] = {
 	NULL
 };
 
+static const char message_advice_ambiguous_remote_tracking_branch[] =
+	N_("If you meant to create a worktree from a remote tracking branch on,\n"
+	   "e.g. 'origin', you can do so by fully qualifying the name:\n"
+	   "\n"
+	   "    git worktree add <path> origin/<name>\n"
+	   "\n"
+	   "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+	   "one remote, e.g. the 'origin' remote, consider setting\n"
+	   "checkout.defaultRemote=origin in your config.");
+
 struct add_opts {
 	int force;
 	int detach;
@@ -764,7 +774,7 @@ static int dwim_orphan(const struct add_opts *opts, int opt_track, int remote)
 	return 1;
 }
 
-static char *dwim_branch(const char *path, char **new_branch)
+static char *dwim_branch(const struct add_opts *opts, const char *path, char **new_branch)
 {
 	int n;
 	int branch_exists;
@@ -781,8 +791,14 @@ static char *dwim_branch(const char *path, char **new_branch)
 
 	*new_branch = branchname;
 	if (guess_remote) {
+		int num_matches = 0;
 		struct object_id oid;
-		char *remote = unique_tracking_name(*new_branch, &oid, NULL);
+		char *remote = unique_tracking_name(*new_branch, &oid, &num_matches);
+		if (!opts->quiet && !remote && num_matches > 1) {
+			if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+				advise(_(message_advice_ambiguous_remote_tracking_branch));
+			warning(_("'%s' matched multiple (%d) remote tracking branches\n"), branchname, num_matches);
+		}
 		return remote;
 	}
 	return NULL;
@@ -890,7 +906,7 @@ static int add(int ac, const char **av, const char *prefix,
 		opts.orphan = dwim_orphan(&opts, !!opt_track, 0);
 	} else if (ac < 2) {
 		/* DWIM: Guess branch name from path. */
-		char *s = dwim_branch(path, &new_branch_to_free);
+		char *s = dwim_branch(&opts, path, &new_branch_to_free);
 		if (s)
 			branch = branch_to_free = s;
 		new_branch = new_branch_to_free;
@@ -904,10 +920,16 @@ static int add(int ac, const char **av, const char *prefix,
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL);
+			int num_matches = 0;
+			remote = unique_tracking_name(branch, &oid, &num_matches);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
+			} else if (num_matches > 1) {
+				if (!opts.quiet && advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME)) {
+					advise(_(message_advice_ambiguous_remote_tracking_branch));
+				}
+				die(_("'%s' matched multiple (%d) remote tracking branches"), branch, num_matches);
 			}
 		}
 
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 87b926728a..4d21c8eba4 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -624,12 +624,12 @@ test_expect_success '"add" <path> <branch> dwims' '
 test_expect_success '"add" <path> <branch> dwims with checkout.defaultRemote' '
 	test_when_finished rm -rf repo_upstream repo_dwim foo &&
 	setup_remote_repo repo_upstream repo_dwim &&
-	git init repo_dwim &&
 	(
 		cd repo_dwim &&
 		git remote add repo_upstream2 ../repo_upstream &&
 		git fetch repo_upstream2 &&
-		test_must_fail git worktree add ../foo foo &&
+		test_must_fail git worktree add ../foo foo 2>error.actual &&
+		test_grep "matched multiple (2) remote tracking branches" error.actual &&
 		git -c checkout.defaultRemote=repo_upstream worktree add ../foo foo &&
 		git status -uno --porcelain >status.actual &&
 		test_must_be_empty status.actual
@@ -669,6 +669,23 @@ test_expect_success 'git worktree add --guess-remote sets up tracking' '
 		test_cmp_rev refs/remotes/repo_a/foo refs/heads/foo
 	)
 '
+test_expect_success 'git worktree add --guess-remote with ambiguous name' '
+	test_when_finished rm -rf repo_a repo_b foo &&
+	setup_remote_repo repo_a repo_b &&
+	(
+		cd repo_b &&
+		git remote add upstream2 ../repo_a &&
+		git fetch upstream2 &&
+		git worktree add --guess-remote ../foo 2>actual &&
+		test_grep "matched multiple (2) remote tracking branches" actual
+	) &&
+	(
+		cd foo &&
+		test_must_fail git config "branch.foo.remote" &&
+		test_must_fail git config "branch.foo.merge" &&
+		test_cmp_rev refs/heads/main refs/heads/foo
+	)
+'
 test_expect_success 'git worktree add --guess-remote sets up tracking (quiet)' '
 	test_when_finished rm -rf repo_a repo_b foo &&
 	setup_remote_repo repo_a repo_b &&

base-commit: 010afd3166ddc64c9863b1506f12cbcdda0d4ea1

builtin/worktree.c, t/t2400-worktree-add.sh

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 654d27c3e1..b29c3a3755 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -64,6 +64,19 @@
 	"\n" \
 	"    git worktree add --orphan %s\n")
 
+#define WORKTREE_ADD_AMBIGUOUS_REMOTE_BRANCH_NAME_HINT_TEXT \
+	_("Matched multiple remote tracking branches, you can list them by:\n" \
+	"\n" \
+	"    git branch -r --list \"*/%s\"\n" \
+	"\n" \
+	"If you meant to create a worktree from a remote tracking branch on,\n" \
+	"e.g. 'origin', you can do so by:\n" \
+	"\n" \
+	"    git worktree add -b %s %s origin/%s\n" \
+	"\n" \
+	"If you'd like to always prefer some remote, e.g. 'origin',\n" \
+	"consider setting checkout.defaultRemote=origin in your config.")
+
 static const char * const git_worktree_usage[] = {
 	BUILTIN_WORKTREE_ADD_USAGE,
 	BUILTIN_WORKTREE_LIST_USAGE,
@@ -904,10 +917,18 @@ static int add(int ac, const char **av, const char *prefix,
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL);
+			int num_matches = 0;
+			remote = unique_tracking_name(branch, &oid, &num_matches);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
+			} else if (num_matches > 1) {
+				if (!opts.quiet)
+					advise_if_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME,
+							  WORKTREE_ADD_AMBIGUOUS_REMOTE_BRANCH_NAME_HINT_TEXT,
+							  branch, branch, path, branch);
+				die(_("'%s' matched multiple (%d) remote tracking branches"),
+				    branch, num_matches);
 			}
 		}
 
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 87b926728a..5c105cf252 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -624,12 +624,12 @@ test_expect_success '"add" <path> <branch> dwims' '
 test_expect_success '"add" <path> <branch> dwims with checkout.defaultRemote' '
 	test_when_finished rm -rf repo_upstream repo_dwim foo &&
 	setup_remote_repo repo_upstream repo_dwim &&
-	git init repo_dwim &&
 	(
 		cd repo_dwim &&
 		git remote add repo_upstream2 ../repo_upstream &&
 		git fetch repo_upstream2 &&
-		test_must_fail git worktree add ../foo foo &&
+		test_must_fail git worktree add ../foo foo 2>error.actual &&
+		test_grep "matched multiple (2) remote tracking branches" error.actual &&
 		git -c checkout.defaultRemote=repo_upstream worktree add ../foo foo &&
 		git status -uno --porcelain >status.actual &&
 		test_must_be_empty status.actual

base-commit: 010afd3166ddc64c9863b1506f12cbcdda0d4ea1

builtin/worktree.c, t/t2400-worktree-add.sh

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 654d27c3e1..b29c3a3755 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -64,6 +64,19 @@
 	"\n" \
 	"    git worktree add --orphan %s\n")
 
+#define WORKTREE_ADD_AMBIGUOUS_REMOTE_BRANCH_NAME_HINT_TEXT \
+	_("Matched multiple remote tracking branches, you can list them by:\n" \
+	"\n" \
+	"    git branch -r --list \"*/%s\"\n" \
+	"\n" \
+	"If you meant to create a worktree from a remote tracking branch on,\n" \
+	"e.g. 'origin', you can do so by:\n" \
+	"\n" \
+	"    git worktree add -b %s %s origin/%s\n" \
+	"\n" \
+	"If you'd like to always prefer some remote, e.g. 'origin',\n" \
+	"consider setting checkout.defaultRemote=origin in your config.")
+
 static const char * const git_worktree_usage[] = {
 	BUILTIN_WORKTREE_ADD_USAGE,
 	BUILTIN_WORKTREE_LIST_USAGE,
@@ -904,10 +917,18 @@ static int add(int ac, const char **av, const char *prefix,
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL);
+			int num_matches = 0;
+			remote = unique_tracking_name(branch, &oid, &num_matches);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
+			} else if (num_matches > 1) {
+				if (!opts.quiet)
+					advise_if_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME,
+							  WORKTREE_ADD_AMBIGUOUS_REMOTE_BRANCH_NAME_HINT_TEXT,
+							  branch, branch, path, branch);
+				die(_("'%s' matched multiple (%d) remote tracking branches"),
+				    branch, num_matches);
 			}
 		}
 
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 87b926728a..5c105cf252 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -624,12 +624,12 @@ test_expect_success '"add" <path> <branch> dwims' '
 test_expect_success '"add" <path> <branch> dwims with checkout.defaultRemote' '
 	test_when_finished rm -rf repo_upstream repo_dwim foo &&
 	setup_remote_repo repo_upstream repo_dwim &&
-	git init repo_dwim &&
 	(
 		cd repo_dwim &&
 		git remote add repo_upstream2 ../repo_upstream &&
 		git fetch repo_upstream2 &&
-		test_must_fail git worktree add ../foo foo &&
+		test_must_fail git worktree add ../foo foo 2>error.actual &&
+		test_grep "matched multiple (2) remote tracking branches" error.actual &&
 		git -c checkout.defaultRemote=repo_upstream worktree add ../foo foo &&
 		git status -uno --porcelain >status.actual &&
 		test_must_be_empty status.actual

base-commit: 010afd3166ddc64c9863b1506f12cbcdda0d4ea1

builtin/worktree.c, t/t2400-worktree-add.sh

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 654d27c3e1..b29c3a3755 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -64,6 +64,19 @@
 	"\n" \
 	"    git worktree add --orphan %s\n")
 
+#define WORKTREE_ADD_AMBIGUOUS_REMOTE_BRANCH_NAME_HINT_TEXT \
+	_("Matched multiple remote tracking branches, you can list them by:\n" \
+	"\n" \
+	"    git branch -r --list \"*/%s\"\n" \
+	"\n" \
+	"If you meant to create a worktree from a remote tracking branch on,\n" \
+	"e.g. 'origin', you can do so by:\n" \
+	"\n" \
+	"    git worktree add -b %s %s origin/%s\n" \
+	"\n" \
+	"If you'd like to always prefer some remote, e.g. 'origin',\n" \
+	"consider setting checkout.defaultRemote=origin in your config.")
+
 static const char * const git_worktree_usage[] = {
 	BUILTIN_WORKTREE_ADD_USAGE,
 	BUILTIN_WORKTREE_LIST_USAGE,
@@ -904,10 +917,18 @@ static int add(int ac, const char **av, const char *prefix,
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL);
+			int num_matches = 0;
+			remote = unique_tracking_name(branch, &oid, &num_matches);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
+			} else if (num_matches > 1) {
+				if (!opts.quiet)
+					advise_if_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME,
+							  WORKTREE_ADD_AMBIGUOUS_REMOTE_BRANCH_NAME_HINT_TEXT,
+							  branch, branch, path, branch);
+				die(_("'%s' matched multiple (%d) remote tracking branches"),
+				    branch, num_matches);
 			}
 		}
 
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 87b926728a..5c105cf252 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -624,12 +624,12 @@ test_expect_success '"add" <path> <branch> dwims' '
 test_expect_success '"add" <path> <branch> dwims with checkout.defaultRemote' '
 	test_when_finished rm -rf repo_upstream repo_dwim foo &&
 	setup_remote_repo repo_upstream repo_dwim &&
-	git init repo_dwim &&
 	(
 		cd repo_dwim &&
 		git remote add repo_upstream2 ../repo_upstream &&
 		git fetch repo_upstream2 &&
-		test_must_fail git worktree add ../foo foo &&
+		test_must_fail git worktree add ../foo foo 2>error.actual &&
+		test_grep "matched multiple (2) remote tracking branches" error.actual &&
 		git -c checkout.defaultRemote=repo_upstream worktree add ../foo foo &&
 		git status -uno --porcelain >status.actual &&
 		test_must_be_empty status.actual

base-commit: 010afd3166ddc64c9863b1506f12cbcdda0d4ea1

diff --git c/builtin/checkout.c w/builtin/checkout.c
index 55e3a89a85..8d61973a11 100644
--- c/builtin/checkout.c
+++ w/builtin/checkout.c
@@ -1343,13 +1343,50 @@ enum checkout_command {
 	CHECKOUT_RESTORE = 3,
 };
 
+static void be_explicit(enum checkout_command which_command,
+			const struct string_list *matched_remote_names)
+{
+	const char *cmdname;
+	struct string_list_item *item;
+
+	switch (which_command) {
+	case CHECKOUT_CHECKOUT:
+		cmdname = "checkout";
+		break;
+	case CHECKOUT_SWITCH:
+		cmdname = "switch";
+		break;
+	default:
+		BUG("command <%d> should not reach parse_remote_branch",
+		     which_command);
+		break;
+	}
+
+	advise(_("Branches with the same name appears in multiple remotes:"));
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+		 "you can do so by fully qualifying the name with the --track option:\n"
+		 "\n"
+		 "    git %s --track origin/<name>\n"
+		 "\n"
+		 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+		 "one remote, e.g. the 'origin' remote, consider setting\n"
+		 "checkout.defaultRemote=origin in your config."),
+	       cmdname);
+}
+
 static char *parse_remote_branch(const char *arg,
 				 struct object_id *rev,
 				 int could_be_checkout_paths,
 				 enum checkout_command which_command)
 {
 	int num_matches = 0;
-	char *remote = unique_tracking_name(arg, rev, &num_matches);
+	struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+	char *remote = unique_tracking_name(arg, rev, &num_matches,
+					    &matched_remote_names);
 
 	if (remote && could_be_checkout_paths) {
 		die(_("'%s' could be both a local file and a tracking branch.\n"
@@ -1358,37 +1395,14 @@ static char *parse_remote_branch(const char *arg,
 	}
 
 	if (!remote && num_matches > 1) {
-	    if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME)) {
-		    const char *cmdname;
-
-		    switch (which_command) {
-		    case CHECKOUT_CHECKOUT:
-			    cmdname = "checkout";
-			    break;
-		    case CHECKOUT_SWITCH:
-			    cmdname = "switch";
-			    break;
-		    default:
-			    BUG("command <%d> should not reach parse_remote_branch",
-				which_command);
-			    break;
-		    }
-
-		    advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
-			     "you can do so by fully qualifying the name with the --track option:\n"
-			     "\n"
-			     "    git %s --track origin/<name>\n"
-			     "\n"
-			     "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
-			     "one remote, e.g. the 'origin' remote, consider setting\n"
-			     "checkout.defaultRemote=origin in your config."),
-			   cmdname);
-	    }
-
-	    die(_("'%s' matched multiple (%d) remote tracking branches"),
-		arg, num_matches);
+		if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+			be_explicit(which_command, &matched_remote_names);
+		die(_("'%s' matched multiple (%d) remote tracking branches"),
+		    arg, num_matches);
 	}
 
+	string_list_clear(&matched_remote_names, 0);
+
 	return remote;
 }
 
diff --git c/builtin/worktree.c w/builtin/worktree.c
index 654d27c3e1..22c8e5e131 100644
--- c/builtin/worktree.c
+++ w/builtin/worktree.c
@@ -782,7 +782,7 @@ static char *dwim_branch(const char *path, char **new_branch)
 	*new_branch = branchname;
 	if (guess_remote) {
 		struct object_id oid;
-		char *remote = unique_tracking_name(*new_branch, &oid, NULL);
+		char *remote = unique_tracking_name(*new_branch, &oid, NULL, NULL);
 		return remote;
 	}
 	return NULL;
@@ -904,7 +904,7 @@ static int add(int ac, const char **av, const char *prefix,
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL);
+			remote = unique_tracking_name(branch, &oid, NULL, NULL);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
diff --git c/checkout.c w/checkout.c
index 1588b116ee..2806b783ec 100644
--- c/checkout.c
+++ w/checkout.c
@@ -8,6 +8,7 @@
 #include "checkout.h"
 #include "config.h"
 #include "strbuf.h"
+#include "string-list.h"
 
 struct tracking_name_data {
 	/* const */ char *src_ref;
@@ -17,6 +18,7 @@ struct tracking_name_data {
 	const char *default_remote;
 	char *default_dst_ref;
 	struct object_id *default_dst_oid;
+	struct string_list **remote_names;
 };
 
 #define TRACKING_NAME_DATA_INIT { 0 }
@@ -39,6 +41,8 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 		oidcpy(dst, cb->dst_oid);
 		cb->default_dst_oid = dst;
 	}
+	if (cb->remote_names)
+		string_list_append(*cb->remote_names, remote->name);
 	if (cb->dst_ref) {
 		free(query.dst);
 		return 0;
@@ -48,14 +52,20 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 }
 
 char *unique_tracking_name(const char *name, struct object_id *oid,
-			   int *dwim_remotes_matched)
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names)
 {
 	struct tracking_name_data cb_data = TRACKING_NAME_DATA_INIT;
 	const char *default_remote = NULL;
-	if (!repo_config_get_string_tmp(the_repository, "checkout.defaultremote", &default_remote))
+
+	if (!repo_config_get_string_tmp(the_repository,
+					"checkout.defaultremote",
+					&default_remote))
 		cb_data.default_remote = default_remote;
 	cb_data.src_ref = xstrfmt("refs/heads/%s", name);
 	cb_data.dst_oid = oid;
+	if (dwim_remote_names)
+		cb_data.remote_names = &dwim_remote_names;
 	for_each_remote(check_tracking_name, &cb_data);
 	if (dwim_remotes_matched)
 		*dwim_remotes_matched = cb_data.num_matches;
diff --git c/checkout.h w/checkout.h
index 55920e7aeb..0b185a0fc9 100644
--- c/checkout.h
+++ w/checkout.h
@@ -3,6 +3,8 @@
 
 #include "hash.h"
 
+struct string_list;
+
 /*
  * Check if the branch name uniquely matches a branch name on a remote
  * tracking branch.  Return the name of the remote if such a branch
@@ -10,6 +12,7 @@
  */
 char *unique_tracking_name(const char *name,
 			   struct object_id *oid,
-			   int *dwim_remotes_matched);
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names);
 
 #endif /* CHECKOUT_H */

builtin/checkout.c, builtin/worktree.c, checkout.c, checkout.h

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 55e3a89a85..a2749352e6 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1343,13 +1343,51 @@ enum checkout_command {
 	CHECKOUT_RESTORE = 3,
 };
 
+static void be_explicit(const char *branch,
+			enum checkout_command which_command,
+			const struct string_list *matched_remote_names)
+{
+	const char *cmdname;
+	struct string_list_item *item;
+
+	switch (which_command) {
+	case CHECKOUT_CHECKOUT:
+		cmdname = "checkout";
+		break;
+	case CHECKOUT_SWITCH:
+		cmdname = "switch";
+		break;
+	default:
+		BUG("command <%d> should not reach parse_remote_branch",
+		     which_command);
+		break;
+	}
+
+	advise(_("Branches with the same name appears in multiple remotes:"));
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to check out a remote tracking branch on <remote>,\n"
+		 "you can do so by fully qualifying the name with the --track option:\n"
+		 "\n"
+		 "    git %s --track <remote>/%s\n"
+		 "\n"
+		 "If you'd like to always have checkouts of an ambiguous name prefer\n"
+		 "one remote, e.g. the 'origin' remote, consider setting\n"
+		 "checkout.defaultRemote=origin in your config."),
+	       cmdname, branch);
+}
+
 static char *parse_remote_branch(const char *arg,
 				 struct object_id *rev,
 				 int could_be_checkout_paths,
 				 enum checkout_command which_command)
 {
 	int num_matches = 0;
-	char *remote = unique_tracking_name(arg, rev, &num_matches);
+	struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+	char *remote = unique_tracking_name(arg, rev, &num_matches,
+					    &matched_remote_names);
 
 	if (remote && could_be_checkout_paths) {
 		die(_("'%s' could be both a local file and a tracking branch.\n"
@@ -1358,37 +1396,14 @@ static char *parse_remote_branch(const char *arg,
 	}
 
 	if (!remote && num_matches > 1) {
-	    if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME)) {
-		    const char *cmdname;
-
-		    switch (which_command) {
-		    case CHECKOUT_CHECKOUT:
-			    cmdname = "checkout";
-			    break;
-		    case CHECKOUT_SWITCH:
-			    cmdname = "switch";
-			    break;
-		    default:
-			    BUG("command <%d> should not reach parse_remote_branch",
-				which_command);
-			    break;
-		    }
-
-		    advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
-			     "you can do so by fully qualifying the name with the --track option:\n"
-			     "\n"
-			     "    git %s --track origin/<name>\n"
-			     "\n"
-			     "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
-			     "one remote, e.g. the 'origin' remote, consider setting\n"
-			     "checkout.defaultRemote=origin in your config."),
-			   cmdname);
-	    }
-
-	    die(_("'%s' matched multiple (%d) remote tracking branches"),
-		arg, num_matches);
+		if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+			be_explicit(arg, which_command, &matched_remote_names);
+		die(_("'%s' matched multiple (%d) remote tracking branches"),
+		    arg, num_matches);
 	}
 
+	string_list_clear(&matched_remote_names, 0);
+
 	return remote;
 }
 
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 654d27c3e1..22c8e5e131 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -782,7 +782,7 @@ static char *dwim_branch(const char *path, char **new_branch)
 	*new_branch = branchname;
 	if (guess_remote) {
 		struct object_id oid;
-		char *remote = unique_tracking_name(*new_branch, &oid, NULL);
+		char *remote = unique_tracking_name(*new_branch, &oid, NULL, NULL);
 		return remote;
 	}
 	return NULL;
@@ -904,7 +904,7 @@ static int add(int ac, const char **av, const char *prefix,
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL);
+			remote = unique_tracking_name(branch, &oid, NULL, NULL);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
diff --git a/checkout.c b/checkout.c
index 1588b116ee..2806b783ec 100644
--- a/checkout.c
+++ b/checkout.c
@@ -8,6 +8,7 @@
 #include "checkout.h"
 #include "config.h"
 #include "strbuf.h"
+#include "string-list.h"
 
 struct tracking_name_data {
 	/* const */ char *src_ref;
@@ -17,6 +18,7 @@ struct tracking_name_data {
 	const char *default_remote;
 	char *default_dst_ref;
 	struct object_id *default_dst_oid;
+	struct string_list **remote_names;
 };
 
 #define TRACKING_NAME_DATA_INIT { 0 }
@@ -39,6 +41,8 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 		oidcpy(dst, cb->dst_oid);
 		cb->default_dst_oid = dst;
 	}
+	if (cb->remote_names)
+		string_list_append(*cb->remote_names, remote->name);
 	if (cb->dst_ref) {
 		free(query.dst);
 		return 0;
@@ -48,14 +52,20 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 }
 
 char *unique_tracking_name(const char *name, struct object_id *oid,
-			   int *dwim_remotes_matched)
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names)
 {
 	struct tracking_name_data cb_data = TRACKING_NAME_DATA_INIT;
 	const char *default_remote = NULL;
-	if (!repo_config_get_string_tmp(the_repository, "checkout.defaultremote", &default_remote))
+
+	if (!repo_config_get_string_tmp(the_repository,
+					"checkout.defaultremote",
+					&default_remote))
 		cb_data.default_remote = default_remote;
 	cb_data.src_ref = xstrfmt("refs/heads/%s", name);
 	cb_data.dst_oid = oid;
+	if (dwim_remote_names)
+		cb_data.remote_names = &dwim_remote_names;
 	for_each_remote(check_tracking_name, &cb_data);
 	if (dwim_remotes_matched)
 		*dwim_remotes_matched = cb_data.num_matches;
diff --git a/checkout.h b/checkout.h
index 55920e7aeb..0b185a0fc9 100644
--- a/checkout.h
+++ b/checkout.h
@@ -3,6 +3,8 @@
 
 #include "hash.h"
 
+struct string_list;
+
 /*
  * Check if the branch name uniquely matches a branch name on a remote
  * tracking branch.  Return the name of the remote if such a branch
@@ -10,6 +12,7 @@
  */
 char *unique_tracking_name(const char *name,
 			   struct object_id *oid,
-			   int *dwim_remotes_matched);
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names);
 
 #endif /* CHECKOUT_H */

builtin/worktree.c, t/t2400-worktree-add.sh

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 22c8e5e131..30d7a8c340 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -788,6 +788,25 @@ static char *dwim_branch(const char *path, char **new_branch)
 	return NULL;
 }
 
+static void advise_ambiguous_remote(const char *path, const char *branch,
+				    const struct string_list *matched_remote_names)
+{
+	struct string_list_item *item;
+
+	advise(_("Branches with the same name appears in multiple remotes:"));
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to create a worktree from a remote tracking branch on\n"
+		 "<remote>, you can do so by:\n"
+		 "\n"
+		 "    git worktree add -b %s %s <remote>/%s\n"
+		 "\n"
+		 "If you'd like to always prefer some remote, e.g. 'origin',\n"
+		 "consider setting checkout.defaultRemote=origin in your config."),
+	       branch, path, branch);
+}
+
 static int add(int ac, const char **av, const char *prefix,
 	       struct repository *repo UNUSED)
 {
@@ -900,15 +919,26 @@ static int add(int ac, const char **av, const char *prefix,
 	} else if (ac == 2) {
 		struct object_id oid;
 		struct commit *commit;
-		char *remote;
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL, NULL);
+			char *remote;
+			int num_matches = 0;
+			struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+			remote = unique_tracking_name(branch, &oid, &num_matches,
+						      &matched_remote_names);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
+			} else if (num_matches > 1) {
+				if (!opts.quiet &&
+				    advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+					advise_ambiguous_remote(path, branch, &matched_remote_names);
+				die(_("'%s' matched multiple (%d) remote tracking branches"),
+				    branch, num_matches);
 			}
+			string_list_clear(&matched_remote_names, 0);
 		}
 
 		if (!strcmp(branch, "HEAD"))
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 87b926728a..5c105cf252 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -624,12 +624,12 @@ test_expect_success '"add" <path> <branch> dwims' '
 test_expect_success '"add" <path> <branch> dwims with checkout.defaultRemote' '
 	test_when_finished rm -rf repo_upstream repo_dwim foo &&
 	setup_remote_repo repo_upstream repo_dwim &&
-	git init repo_dwim &&
 	(
 		cd repo_dwim &&
 		git remote add repo_upstream2 ../repo_upstream &&
 		git fetch repo_upstream2 &&
-		test_must_fail git worktree add ../foo foo &&
+		test_must_fail git worktree add ../foo foo 2>error.actual &&
+		test_grep "matched multiple (2) remote tracking branches" error.actual &&
 		git -c checkout.defaultRemote=repo_upstream worktree add ../foo foo &&
 		git status -uno --porcelain >status.actual &&
 		test_must_be_empty status.actual

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 55e3a89a85..650eda735f 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1343,6 +1343,34 @@ enum checkout_command {
 	CHECKOUT_RESTORE = 3,
 };
 
+static void advice_disambiguating_remotes(enum checkout_command which_command)
+{
+	const char *cmdname;
+
+	switch (which_command) {
+	case CHECKOUT_CHECKOUT:
+		cmdname = "checkout";
+		break;
+	case CHECKOUT_SWITCH:
+		cmdname = "switch";
+		break;
+	default:
+		BUG("command <%d> should not reach parse_remote_branch",
+		    which_command);
+		break;
+	}
+
+	advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+		 "you can do so by fully qualifying the name with the --track option:\n"
+		 "\n"
+		 "    git %s --track origin/<name>\n"
+		 "\n"
+		 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+		 "one remote, e.g. the 'origin' remote, consider setting\n"
+		 "checkout.defaultRemote=origin in your config."),
+	       cmdname);
+}
+
 static char *parse_remote_branch(const char *arg,
 				 struct object_id *rev,
 				 int could_be_checkout_paths,
@@ -1358,35 +1386,11 @@ static char *parse_remote_branch(const char *arg,
 	}
 
 	if (!remote && num_matches > 1) {
-	    if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME)) {
-		    const char *cmdname;
-
-		    switch (which_command) {
-		    case CHECKOUT_CHECKOUT:
-			    cmdname = "checkout";
-			    break;
-		    case CHECKOUT_SWITCH:
-			    cmdname = "switch";
-			    break;
-		    default:
-			    BUG("command <%d> should not reach parse_remote_branch",
-				which_command);
-			    break;
-		    }
-
-		    advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
-			     "you can do so by fully qualifying the name with the --track option:\n"
-			     "\n"
-			     "    git %s --track origin/<name>\n"
-			     "\n"
-			     "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
-			     "one remote, e.g. the 'origin' remote, consider setting\n"
-			     "checkout.defaultRemote=origin in your config."),
-			   cmdname);
-	    }
-
-	    die(_("'%s' matched multiple (%d) remote tracking branches"),
-		arg, num_matches);
+		if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+			advice_disambiguating_remotes(which_command);
+
+		die(_("'%s' matched multiple (%d) remote tracking branches"),
+		    arg, num_matches);
 	}
 
 	return remote;

builtin/checkout.c, builtin/worktree.c, checkout.c, checkout.h

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 650eda735f..35227f7cbd 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1343,9 +1343,12 @@ enum checkout_command {
 	CHECKOUT_RESTORE = 3,
 };
 
-static void advice_disambiguating_remotes(enum checkout_command which_command)
+static void advise_disambiguating_remotes(enum checkout_command which_command,
+					  const char *branch,
+					  const struct string_list *matched_remote_names)
 {
 	const char *cmdname;
+	struct string_list_item *item;
 
 	switch (which_command) {
 	case CHECKOUT_CHECKOUT:
@@ -1360,15 +1363,19 @@ static void advice_disambiguating_remotes(enum checkout_command which_command)
 		break;
 	}
 
-	advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+	advise(_("Branches with the same name appears in multiple remotes:"));
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to check out a remote tracking branch on <remote>,\n"
 		 "you can do so by fully qualifying the name with the --track option:\n"
 		 "\n"
-		 "    git %s --track origin/<name>\n"
+		 "    git %s --track <remote>/%s\n"
 		 "\n"
-		 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+		 "If you'd like to always have checkouts of an ambiguous name prefer\n"
 		 "one remote, e.g. the 'origin' remote, consider setting\n"
 		 "checkout.defaultRemote=origin in your config."),
-	       cmdname);
+	       cmdname, branch);
 }
 
 static char *parse_remote_branch(const char *arg,
@@ -1377,7 +1384,10 @@ static char *parse_remote_branch(const char *arg,
 				 enum checkout_command which_command)
 {
 	int num_matches = 0;
-	char *remote = unique_tracking_name(arg, rev, &num_matches);
+	struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+	char *remote = unique_tracking_name(arg, rev, &num_matches,
+					    &matched_remote_names);
 
 	if (remote && could_be_checkout_paths) {
 		die(_("'%s' could be both a local file and a tracking branch.\n"
@@ -1387,12 +1397,14 @@ static char *parse_remote_branch(const char *arg,
 
 	if (!remote && num_matches > 1) {
 		if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
-			advice_disambiguating_remotes(which_command);
-
+			advise_disambiguating_remotes(which_command, arg,
+						      &matched_remote_names);
 		die(_("'%s' matched multiple (%d) remote tracking branches"),
 		    arg, num_matches);
 	}
 
+	string_list_clear(&matched_remote_names, 0);
+
 	return remote;
 }
 
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 654d27c3e1..22c8e5e131 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -782,7 +782,7 @@ static char *dwim_branch(const char *path, char **new_branch)
 	*new_branch = branchname;
 	if (guess_remote) {
 		struct object_id oid;
-		char *remote = unique_tracking_name(*new_branch, &oid, NULL);
+		char *remote = unique_tracking_name(*new_branch, &oid, NULL, NULL);
 		return remote;
 	}
 	return NULL;
@@ -904,7 +904,7 @@ static int add(int ac, const char **av, const char *prefix,
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL);
+			remote = unique_tracking_name(branch, &oid, NULL, NULL);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
diff --git a/checkout.c b/checkout.c
index 1588b116ee..2806b783ec 100644
--- a/checkout.c
+++ b/checkout.c
@@ -8,6 +8,7 @@
 #include "checkout.h"
 #include "config.h"
 #include "strbuf.h"
+#include "string-list.h"
 
 struct tracking_name_data {
 	/* const */ char *src_ref;
@@ -17,6 +18,7 @@ struct tracking_name_data {
 	const char *default_remote;
 	char *default_dst_ref;
 	struct object_id *default_dst_oid;
+	struct string_list **remote_names;
 };
 
 #define TRACKING_NAME_DATA_INIT { 0 }
@@ -39,6 +41,8 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 		oidcpy(dst, cb->dst_oid);
 		cb->default_dst_oid = dst;
 	}
+	if (cb->remote_names)
+		string_list_append(*cb->remote_names, remote->name);
 	if (cb->dst_ref) {
 		free(query.dst);
 		return 0;
@@ -48,14 +52,20 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 }
 
 char *unique_tracking_name(const char *name, struct object_id *oid,
-			   int *dwim_remotes_matched)
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names)
 {
 	struct tracking_name_data cb_data = TRACKING_NAME_DATA_INIT;
 	const char *default_remote = NULL;
-	if (!repo_config_get_string_tmp(the_repository, "checkout.defaultremote", &default_remote))
+
+	if (!repo_config_get_string_tmp(the_repository,
+					"checkout.defaultremote",
+					&default_remote))
 		cb_data.default_remote = default_remote;
 	cb_data.src_ref = xstrfmt("refs/heads/%s", name);
 	cb_data.dst_oid = oid;
+	if (dwim_remote_names)
+		cb_data.remote_names = &dwim_remote_names;
 	for_each_remote(check_tracking_name, &cb_data);
 	if (dwim_remotes_matched)
 		*dwim_remotes_matched = cb_data.num_matches;
diff --git a/checkout.h b/checkout.h
index 55920e7aeb..0b185a0fc9 100644
--- a/checkout.h
+++ b/checkout.h
@@ -3,6 +3,8 @@
 
 #include "hash.h"
 
+struct string_list;
+
 /*
  * Check if the branch name uniquely matches a branch name on a remote
  * tracking branch.  Return the name of the remote if such a branch
@@ -10,6 +12,7 @@
  */
 char *unique_tracking_name(const char *name,
 			   struct object_id *oid,
-			   int *dwim_remotes_matched);
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names);
 
 #endif /* CHECKOUT_H */

builtin/worktree.c, t/t2400-worktree-add.sh

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 22c8e5e131..8286c283e0 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -788,6 +788,25 @@ static char *dwim_branch(const char *path, char **new_branch)
 	return NULL;
 }
 
+static void advise_disambiguating_remotes(const char *path, const char *branch,
+					  const struct string_list *matched_remote_names)
+{
+	struct string_list_item *item;
+
+	advise(_("Branches with the same name appears in multiple remotes:"));
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to create a worktree from a remote tracking branch on\n"
+		 "<remote>, you can do so by:\n"
+		 "\n"
+		 "    git worktree add -b %s %s <remote>/%s\n"
+		 "\n"
+		 "If you'd like to always prefer some remote, e.g. 'origin',\n"
+		 "consider setting checkout.defaultRemote=origin in your config."),
+	       branch, path, branch);
+}
+
 static int add(int ac, const char **av, const char *prefix,
 	       struct repository *repo UNUSED)
 {
@@ -900,15 +919,27 @@ static int add(int ac, const char **av, const char *prefix,
 	} else if (ac == 2) {
 		struct object_id oid;
 		struct commit *commit;
-		char *remote;
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL, NULL);
+			char *remote;
+			int num_matches = 0;
+			struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+			remote = unique_tracking_name(branch, &oid, &num_matches,
+						      &matched_remote_names);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
+			} else if (num_matches > 1) {
+				if (!opts.quiet &&
+				    advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+					advise_disambiguating_remotes(path, branch,
+								      &matched_remote_names);
+				die(_("'%s' matched multiple (%d) remote tracking branches"),
+				    branch, num_matches);
 			}
+			string_list_clear(&matched_remote_names, 0);
 		}
 
 		if (!strcmp(branch, "HEAD"))
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 87b926728a..5c105cf252 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -624,12 +624,12 @@ test_expect_success '"add" <path> <branch> dwims' '
 test_expect_success '"add" <path> <branch> dwims with checkout.defaultRemote' '
 	test_when_finished rm -rf repo_upstream repo_dwim foo &&
 	setup_remote_repo repo_upstream repo_dwim &&
-	git init repo_dwim &&
 	(
 		cd repo_dwim &&
 		git remote add repo_upstream2 ../repo_upstream &&
 		git fetch repo_upstream2 &&
-		test_must_fail git worktree add ../foo foo &&
+		test_must_fail git worktree add ../foo foo 2>error.actual &&
+		test_grep "matched multiple (2) remote tracking branches" error.actual &&
 		git -c checkout.defaultRemote=repo_upstream worktree add ../foo foo &&
 		git status -uno --porcelain >status.actual &&
 		test_must_be_empty status.actual

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 55e3a89a85..650eda735f 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1343,6 +1343,34 @@ enum checkout_command {
 	CHECKOUT_RESTORE = 3,
 };
 
+static void advice_disambiguating_remotes(enum checkout_command which_command)
+{
+	const char *cmdname;
+
+	switch (which_command) {
+	case CHECKOUT_CHECKOUT:
+		cmdname = "checkout";
+		break;
+	case CHECKOUT_SWITCH:
+		cmdname = "switch";
+		break;
+	default:
+		BUG("command <%d> should not reach parse_remote_branch",
+		    which_command);
+		break;
+	}
+
+	advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+		 "you can do so by fully qualifying the name with the --track option:\n"
+		 "\n"
+		 "    git %s --track origin/<name>\n"
+		 "\n"
+		 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+		 "one remote, e.g. the 'origin' remote, consider setting\n"
+		 "checkout.defaultRemote=origin in your config."),
+	       cmdname);
+}
+
 static char *parse_remote_branch(const char *arg,
 				 struct object_id *rev,
 				 int could_be_checkout_paths,
@@ -1358,35 +1386,11 @@ static char *parse_remote_branch(const char *arg,
 	}
 
 	if (!remote && num_matches > 1) {
-	    if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME)) {
-		    const char *cmdname;
-
-		    switch (which_command) {
-		    case CHECKOUT_CHECKOUT:
-			    cmdname = "checkout";
-			    break;
-		    case CHECKOUT_SWITCH:
-			    cmdname = "switch";
-			    break;
-		    default:
-			    BUG("command <%d> should not reach parse_remote_branch",
-				which_command);
-			    break;
-		    }
-
-		    advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
-			     "you can do so by fully qualifying the name with the --track option:\n"
-			     "\n"
-			     "    git %s --track origin/<name>\n"
-			     "\n"
-			     "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
-			     "one remote, e.g. the 'origin' remote, consider setting\n"
-			     "checkout.defaultRemote=origin in your config."),
-			   cmdname);
-	    }
-
-	    die(_("'%s' matched multiple (%d) remote tracking branches"),
-		arg, num_matches);
+		if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+			advice_disambiguating_remotes(which_command);
+
+		die(_("'%s' matched multiple (%d) remote tracking branches"),
+		    arg, num_matches);
 	}
 
 	return remote;

builtin/checkout.c, builtin/worktree.c, checkout.c, checkout.h

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 650eda735f..07373615d8 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1343,9 +1343,12 @@ enum checkout_command {
 	CHECKOUT_RESTORE = 3,
 };
 
-static void advice_disambiguating_remotes(enum checkout_command which_command)
+static void advise_disambiguating_remotes(enum checkout_command which_command,
+					  const char *branch,
+					  const struct string_list *matched_remote_names)
 {
 	const char *cmdname;
+	struct string_list_item *item;
 
 	switch (which_command) {
 	case CHECKOUT_CHECKOUT:
@@ -1360,15 +1363,19 @@ static void advice_disambiguating_remotes(enum checkout_command which_command)
 		break;
 	}
 
-	advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+	advise(_("Branch name '%s' appears in multiple remotes:"), branch);
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to check out a remote tracking branch on <remote>,\n"
 		 "you can do so by fully qualifying the name with the --track option:\n"
 		 "\n"
-		 "    git %s --track origin/<name>\n"
+		 "    git %s --track <remote>/%s\n"
 		 "\n"
-		 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+		 "If you'd like to always have checkouts of an ambiguous name prefer\n"
 		 "one remote, e.g. the 'origin' remote, consider setting\n"
 		 "checkout.defaultRemote=origin in your config."),
-	       cmdname);
+	       cmdname, branch);
 }
 
 static char *parse_remote_branch(const char *arg,
@@ -1377,7 +1384,10 @@ static char *parse_remote_branch(const char *arg,
 				 enum checkout_command which_command)
 {
 	int num_matches = 0;
-	char *remote = unique_tracking_name(arg, rev, &num_matches);
+	struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+	char *remote = unique_tracking_name(arg, rev, &num_matches,
+					    &matched_remote_names);
 
 	if (remote && could_be_checkout_paths) {
 		die(_("'%s' could be both a local file and a tracking branch.\n"
@@ -1387,12 +1397,14 @@ static char *parse_remote_branch(const char *arg,
 
 	if (!remote && num_matches > 1) {
 		if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
-			advice_disambiguating_remotes(which_command);
-
+			advise_disambiguating_remotes(which_command, arg,
+						      &matched_remote_names);
 		die(_("'%s' matched multiple (%d) remote tracking branches"),
 		    arg, num_matches);
 	}
 
+	string_list_clear(&matched_remote_names, 0);
+
 	return remote;
 }
 
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 654d27c3e1..22c8e5e131 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -782,7 +782,7 @@ static char *dwim_branch(const char *path, char **new_branch)
 	*new_branch = branchname;
 	if (guess_remote) {
 		struct object_id oid;
-		char *remote = unique_tracking_name(*new_branch, &oid, NULL);
+		char *remote = unique_tracking_name(*new_branch, &oid, NULL, NULL);
 		return remote;
 	}
 	return NULL;
@@ -904,7 +904,7 @@ static int add(int ac, const char **av, const char *prefix,
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL);
+			remote = unique_tracking_name(branch, &oid, NULL, NULL);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
diff --git a/checkout.c b/checkout.c
index 1588b116ee..2806b783ec 100644
--- a/checkout.c
+++ b/checkout.c
@@ -8,6 +8,7 @@
 #include "checkout.h"
 #include "config.h"
 #include "strbuf.h"
+#include "string-list.h"
 
 struct tracking_name_data {
 	/* const */ char *src_ref;
@@ -17,6 +18,7 @@ struct tracking_name_data {
 	const char *default_remote;
 	char *default_dst_ref;
 	struct object_id *default_dst_oid;
+	struct string_list **remote_names;
 };
 
 #define TRACKING_NAME_DATA_INIT { 0 }
@@ -39,6 +41,8 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 		oidcpy(dst, cb->dst_oid);
 		cb->default_dst_oid = dst;
 	}
+	if (cb->remote_names)
+		string_list_append(*cb->remote_names, remote->name);
 	if (cb->dst_ref) {
 		free(query.dst);
 		return 0;
@@ -48,14 +52,20 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 }
 
 char *unique_tracking_name(const char *name, struct object_id *oid,
-			   int *dwim_remotes_matched)
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names)
 {
 	struct tracking_name_data cb_data = TRACKING_NAME_DATA_INIT;
 	const char *default_remote = NULL;
-	if (!repo_config_get_string_tmp(the_repository, "checkout.defaultremote", &default_remote))
+
+	if (!repo_config_get_string_tmp(the_repository,
+					"checkout.defaultremote",
+					&default_remote))
 		cb_data.default_remote = default_remote;
 	cb_data.src_ref = xstrfmt("refs/heads/%s", name);
 	cb_data.dst_oid = oid;
+	if (dwim_remote_names)
+		cb_data.remote_names = &dwim_remote_names;
 	for_each_remote(check_tracking_name, &cb_data);
 	if (dwim_remotes_matched)
 		*dwim_remotes_matched = cb_data.num_matches;
diff --git a/checkout.h b/checkout.h
index 55920e7aeb..0b185a0fc9 100644
--- a/checkout.h
+++ b/checkout.h
@@ -3,6 +3,8 @@
 
 #include "hash.h"
 
+struct string_list;
+
 /*
  * Check if the branch name uniquely matches a branch name on a remote
  * tracking branch.  Return the name of the remote if such a branch
@@ -10,6 +12,7 @@
  */
 char *unique_tracking_name(const char *name,
 			   struct object_id *oid,
-			   int *dwim_remotes_matched);
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names);
 
 #endif /* CHECKOUT_H */

builtin/worktree.c, t/t2400-worktree-add.sh

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 22c8e5e131..320b18873d 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -788,6 +788,25 @@ static char *dwim_branch(const char *path, char **new_branch)
 	return NULL;
 }
 
+static void advise_disambiguating_remotes(const char *path, const char *branch,
+					  const struct string_list *matched_remote_names)
+{
+	struct string_list_item *item;
+
+	advise(_("Branch name '%s' appears in multiple remotes:"), branch);
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to create a worktree from a remote tracking branch on\n"
+		 "<remote>, you can do so by:\n"
+		 "\n"
+		 "    git worktree add -b %s %s <remote>/%s\n"
+		 "\n"
+		 "If you'd like to always prefer some remote, e.g. 'origin',\n"
+		 "consider setting checkout.defaultRemote=origin in your config."),
+	       branch, path, branch);
+}
+
 static int add(int ac, const char **av, const char *prefix,
 	       struct repository *repo UNUSED)
 {
@@ -898,17 +917,29 @@ static int add(int ac, const char **av, const char *prefix,
 		/* DWIM: Infer --orphan when repo has no refs. */
 		opts.orphan = (!s) && dwim_orphan(&opts, !!opt_track, 1);
 	} else if (ac == 2) {
-		struct object_id oid;
 		struct commit *commit;
-		char *remote;
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL, NULL);
+			struct object_id oid;
+			char *remote;
+			int num_matches = 0;
+			struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+			remote = unique_tracking_name(branch, &oid, &num_matches,
+						      &matched_remote_names);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
+			} else if (num_matches > 1) {
+				if (!opts.quiet &&
+				    advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+					advise_disambiguating_remotes(path, branch,
+								      &matched_remote_names);
+				die(_("'%s' matched multiple (%d) remote tracking branches"),
+				    branch, num_matches);
 			}
+			string_list_clear(&matched_remote_names, 0);
 		}
 
 		if (!strcmp(branch, "HEAD"))
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 87b926728a..5c105cf252 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -624,12 +624,12 @@ test_expect_success '"add" <path> <branch> dwims' '
 test_expect_success '"add" <path> <branch> dwims with checkout.defaultRemote' '
 	test_when_finished rm -rf repo_upstream repo_dwim foo &&
 	setup_remote_repo repo_upstream repo_dwim &&
-	git init repo_dwim &&
 	(
 		cd repo_dwim &&
 		git remote add repo_upstream2 ../repo_upstream &&
 		git fetch repo_upstream2 &&
-		test_must_fail git worktree add ../foo foo &&
+		test_must_fail git worktree add ../foo foo 2>error.actual &&
+		test_grep "matched multiple (2) remote tracking branches" error.actual &&
 		git -c checkout.defaultRemote=repo_upstream worktree add ../foo foo &&
 		git status -uno --porcelain >status.actual &&
 		test_must_be_empty status.actual

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 55e3a89a85..650eda735f 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1343,6 +1343,34 @@ enum checkout_command {
 	CHECKOUT_RESTORE = 3,
 };
 
+static void advice_disambiguating_remotes(enum checkout_command which_command)
+{
+	const char *cmdname;
+
+	switch (which_command) {
+	case CHECKOUT_CHECKOUT:
+		cmdname = "checkout";
+		break;
+	case CHECKOUT_SWITCH:
+		cmdname = "switch";
+		break;
+	default:
+		BUG("command <%d> should not reach parse_remote_branch",
+		    which_command);
+		break;
+	}
+
+	advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+		 "you can do so by fully qualifying the name with the --track option:\n"
+		 "\n"
+		 "    git %s --track origin/<name>\n"
+		 "\n"
+		 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+		 "one remote, e.g. the 'origin' remote, consider setting\n"
+		 "checkout.defaultRemote=origin in your config."),
+	       cmdname);
+}
+
 static char *parse_remote_branch(const char *arg,
 				 struct object_id *rev,
 				 int could_be_checkout_paths,
@@ -1358,35 +1386,11 @@ static char *parse_remote_branch(const char *arg,
 	}
 
 	if (!remote && num_matches > 1) {
-	    if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME)) {
-		    const char *cmdname;
-
-		    switch (which_command) {
-		    case CHECKOUT_CHECKOUT:
-			    cmdname = "checkout";
-			    break;
-		    case CHECKOUT_SWITCH:
-			    cmdname = "switch";
-			    break;
-		    default:
-			    BUG("command <%d> should not reach parse_remote_branch",
-				which_command);
-			    break;
-		    }
-
-		    advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
-			     "you can do so by fully qualifying the name with the --track option:\n"
-			     "\n"
-			     "    git %s --track origin/<name>\n"
-			     "\n"
-			     "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
-			     "one remote, e.g. the 'origin' remote, consider setting\n"
-			     "checkout.defaultRemote=origin in your config."),
-			   cmdname);
-	    }
-
-	    die(_("'%s' matched multiple (%d) remote tracking branches"),
-		arg, num_matches);
+		if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+			advice_disambiguating_remotes(which_command);
+
+		die(_("'%s' matched multiple (%d) remote tracking branches"),
+		    arg, num_matches);
 	}
 
 	return remote;

builtin/checkout.c, builtin/worktree.c, checkout.c, checkout.h

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 650eda735f..07373615d8 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1343,9 +1343,12 @@ enum checkout_command {
 	CHECKOUT_RESTORE = 3,
 };
 
-static void advice_disambiguating_remotes(enum checkout_command which_command)
+static void advise_disambiguating_remotes(enum checkout_command which_command,
+					  const char *branch,
+					  const struct string_list *matched_remote_names)
 {
 	const char *cmdname;
+	struct string_list_item *item;
 
 	switch (which_command) {
 	case CHECKOUT_CHECKOUT:
@@ -1360,15 +1363,19 @@ static void advice_disambiguating_remotes(enum checkout_command which_command)
 		break;
 	}
 
-	advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+	advise(_("Branch name '%s' appears in multiple remotes:"), branch);
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to check out a remote tracking branch on <remote>,\n"
 		 "you can do so by fully qualifying the name with the --track option:\n"
 		 "\n"
-		 "    git %s --track origin/<name>\n"
+		 "    git %s --track <remote>/%s\n"
 		 "\n"
-		 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+		 "If you'd like to always have checkouts of an ambiguous name prefer\n"
 		 "one remote, e.g. the 'origin' remote, consider setting\n"
 		 "checkout.defaultRemote=origin in your config."),
-	       cmdname);
+	       cmdname, branch);
 }
 
 static char *parse_remote_branch(const char *arg,
@@ -1377,7 +1384,10 @@ static char *parse_remote_branch(const char *arg,
 				 enum checkout_command which_command)
 {
 	int num_matches = 0;
-	char *remote = unique_tracking_name(arg, rev, &num_matches);
+	struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+	char *remote = unique_tracking_name(arg, rev, &num_matches,
+					    &matched_remote_names);
 
 	if (remote && could_be_checkout_paths) {
 		die(_("'%s' could be both a local file and a tracking branch.\n"
@@ -1387,12 +1397,14 @@ static char *parse_remote_branch(const char *arg,
 
 	if (!remote && num_matches > 1) {
 		if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
-			advice_disambiguating_remotes(which_command);
-
+			advise_disambiguating_remotes(which_command, arg,
+						      &matched_remote_names);
 		die(_("'%s' matched multiple (%d) remote tracking branches"),
 		    arg, num_matches);
 	}
 
+	string_list_clear(&matched_remote_names, 0);
+
 	return remote;
 }
 
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 654d27c3e1..22c8e5e131 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -782,7 +782,7 @@ static char *dwim_branch(const char *path, char **new_branch)
 	*new_branch = branchname;
 	if (guess_remote) {
 		struct object_id oid;
-		char *remote = unique_tracking_name(*new_branch, &oid, NULL);
+		char *remote = unique_tracking_name(*new_branch, &oid, NULL, NULL);
 		return remote;
 	}
 	return NULL;
@@ -904,7 +904,7 @@ static int add(int ac, const char **av, const char *prefix,
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL);
+			remote = unique_tracking_name(branch, &oid, NULL, NULL);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
diff --git a/checkout.c b/checkout.c
index 1588b116ee..2806b783ec 100644
--- a/checkout.c
+++ b/checkout.c
@@ -8,6 +8,7 @@
 #include "checkout.h"
 #include "config.h"
 #include "strbuf.h"
+#include "string-list.h"
 
 struct tracking_name_data {
 	/* const */ char *src_ref;
@@ -17,6 +18,7 @@ struct tracking_name_data {
 	const char *default_remote;
 	char *default_dst_ref;
 	struct object_id *default_dst_oid;
+	struct string_list **remote_names;
 };
 
 #define TRACKING_NAME_DATA_INIT { 0 }
@@ -39,6 +41,8 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 		oidcpy(dst, cb->dst_oid);
 		cb->default_dst_oid = dst;
 	}
+	if (cb->remote_names)
+		string_list_append(*cb->remote_names, remote->name);
 	if (cb->dst_ref) {
 		free(query.dst);
 		return 0;
@@ -48,14 +52,20 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 }
 
 char *unique_tracking_name(const char *name, struct object_id *oid,
-			   int *dwim_remotes_matched)
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names)
 {
 	struct tracking_name_data cb_data = TRACKING_NAME_DATA_INIT;
 	const char *default_remote = NULL;
-	if (!repo_config_get_string_tmp(the_repository, "checkout.defaultremote", &default_remote))
+
+	if (!repo_config_get_string_tmp(the_repository,
+					"checkout.defaultremote",
+					&default_remote))
 		cb_data.default_remote = default_remote;
 	cb_data.src_ref = xstrfmt("refs/heads/%s", name);
 	cb_data.dst_oid = oid;
+	if (dwim_remote_names)
+		cb_data.remote_names = &dwim_remote_names;
 	for_each_remote(check_tracking_name, &cb_data);
 	if (dwim_remotes_matched)
 		*dwim_remotes_matched = cb_data.num_matches;
diff --git a/checkout.h b/checkout.h
index 55920e7aeb..0b185a0fc9 100644
--- a/checkout.h
+++ b/checkout.h
@@ -3,6 +3,8 @@
 
 #include "hash.h"
 
+struct string_list;
+
 /*
  * Check if the branch name uniquely matches a branch name on a remote
  * tracking branch.  Return the name of the remote if such a branch
@@ -10,6 +12,7 @@
  */
 char *unique_tracking_name(const char *name,
 			   struct object_id *oid,
-			   int *dwim_remotes_matched);
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names);
 
 #endif /* CHECKOUT_H */

builtin/worktree.c, t/t2400-worktree-add.sh

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 22c8e5e131..320b18873d 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -788,6 +788,25 @@ static char *dwim_branch(const char *path, char **new_branch)
 	return NULL;
 }
 
+static void advise_disambiguating_remotes(const char *path, const char *branch,
+					  const struct string_list *matched_remote_names)
+{
+	struct string_list_item *item;
+
+	advise(_("Branch name '%s' appears in multiple remotes:"), branch);
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to create a worktree from a remote tracking branch on\n"
+		 "<remote>, you can do so by:\n"
+		 "\n"
+		 "    git worktree add -b %s %s <remote>/%s\n"
+		 "\n"
+		 "If you'd like to always prefer some remote, e.g. 'origin',\n"
+		 "consider setting checkout.defaultRemote=origin in your config."),
+	       branch, path, branch);
+}
+
 static int add(int ac, const char **av, const char *prefix,
 	       struct repository *repo UNUSED)
 {
@@ -898,17 +917,29 @@ static int add(int ac, const char **av, const char *prefix,
 		/* DWIM: Infer --orphan when repo has no refs. */
 		opts.orphan = (!s) && dwim_orphan(&opts, !!opt_track, 1);
 	} else if (ac == 2) {
-		struct object_id oid;
 		struct commit *commit;
-		char *remote;
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL, NULL);
+			struct object_id oid;
+			char *remote;
+			int num_matches = 0;
+			struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+			remote = unique_tracking_name(branch, &oid, &num_matches,
+						      &matched_remote_names);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
+			} else if (num_matches > 1) {
+				if (!opts.quiet &&
+				    advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+					advise_disambiguating_remotes(path, branch,
+								      &matched_remote_names);
+				die(_("'%s' matched multiple (%d) remote tracking branches"),
+				    branch, num_matches);
 			}
+			string_list_clear(&matched_remote_names, 0);
 		}
 
 		if (!strcmp(branch, "HEAD"))
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 87b926728a..5c105cf252 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -624,12 +624,12 @@ test_expect_success '"add" <path> <branch> dwims' '
 test_expect_success '"add" <path> <branch> dwims with checkout.defaultRemote' '
 	test_when_finished rm -rf repo_upstream repo_dwim foo &&
 	setup_remote_repo repo_upstream repo_dwim &&
-	git init repo_dwim &&
 	(
 		cd repo_dwim &&
 		git remote add repo_upstream2 ../repo_upstream &&
 		git fetch repo_upstream2 &&
-		test_must_fail git worktree add ../foo foo &&
+		test_must_fail git worktree add ../foo foo 2>error.actual &&
+		test_grep "matched multiple (2) remote tracking branches" error.actual &&
 		git -c checkout.defaultRemote=repo_upstream worktree add ../foo foo &&
 		git status -uno --porcelain >status.actual &&
 		test_must_be_empty status.actual

Documentation/config/worktree.adoc, Documentation/git-worktree.adoc, builtin/worktree.c, t/t2400-worktree-add.sh

diff --git a/Documentation/config/worktree.adoc b/Documentation/config/worktree.adoc
index a248076ea5..0930183b91 100644
--- a/Documentation/config/worktree.adoc
+++ b/Documentation/config/worktree.adoc
@@ -5,8 +5,9 @@
 	set to true, `worktree add` tries to find a remote-tracking
 	branch whose name uniquely matches the new branch name.  If
 	such a branch exists, it is checked out and set as "upstream"
-	for the new branch.  If no such match can be found, it falls
-	back to creating a new branch from the current `HEAD`.
+	for the new branch.  If multiple matches are found, the command
+	fails.  If no such match can be found, it falls back to
+	creating a new branch from the current `HEAD`.
 
 `worktree.useRelativePaths`::
 	Link worktrees using relative paths (when "`true`") or absolute
diff --git a/Documentation/git-worktree.adoc b/Documentation/git-worktree.adoc
index fbf8426cd9..32787eacc3 100644
--- a/Documentation/git-worktree.adoc
+++ b/Documentation/git-worktree.adoc
@@ -219,7 +219,9 @@ To remove a locked worktree, specify `--force` twice.
 	of creating a new branch from `HEAD`, if there exists a tracking
 	branch in exactly one remote matching the basename of _<path>_,
 	base the new branch on the remote-tracking branch, and mark
-	the remote-tracking branch as "upstream" from the new branch.
+	the remote-tracking branch as "upstream" from the new branch. If
+	there are multiple matches, the command fails. If there is no
+	match, the command falls back to creating a new branch from `HEAD`.
 +
 This can also be set up as the default behaviour by using the
 `worktree.guessRemote` config option.
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 320b18873d..07163bf9b7 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -764,7 +764,26 @@ static int dwim_orphan(const struct add_opts *opts, int opt_track, int remote)
 	return 1;
 }
 
-static char *dwim_branch(const char *path, char **new_branch)
+static void advise_disambiguating_remotes(const char *path, const char *branch,
+					  const struct string_list *matched_remote_names)
+{
+	struct string_list_item *item;
+
+	advise(_("Branch name '%s' appears in multiple remotes:"), branch);
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to create a worktree from a remote tracking branch on\n"
+		 "<remote>, you can do so by:\n"
+		 "\n"
+		 "    git worktree add -b %s %s <remote>/%s\n"
+		 "\n"
+		 "If you'd like to always prefer some remote, e.g. 'origin',\n"
+		 "consider setting checkout.defaultRemote=origin in your config."),
+	       branch, path, branch);
+}
+
+static char *dwim_branch(const struct add_opts *opts, const char *path, char **new_branch)
 {
 	int n;
 	int branch_exists;
@@ -782,31 +801,26 @@ static char *dwim_branch(const char *path, char **new_branch)
 	*new_branch = branchname;
 	if (guess_remote) {
 		struct object_id oid;
-		char *remote = unique_tracking_name(*new_branch, &oid, NULL, NULL);
+		char *remote;
+		int num_matches = 0;
+		struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+		remote = unique_tracking_name(*new_branch, &oid, &num_matches,
+					      &matched_remote_names);
+		if (!remote && num_matches > 1) {
+			if (!opts->quiet &&
+			    advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+				advise_disambiguating_remotes(path, *new_branch,
+							      &matched_remote_names);
+			die(_("'%s' matched multiple (%d) remote tracking branches"),
+			    *new_branch, num_matches);
+		}
+		string_list_clear(&matched_remote_names, 0);
 		return remote;
 	}
 	return NULL;
 }
 
-static void advise_disambiguating_remotes(const char *path, const char *branch,
-					  const struct string_list *matched_remote_names)
-{
-	struct string_list_item *item;
-
-	advise(_("Branch name '%s' appears in multiple remotes:"), branch);
-	for_each_string_list_item(item, matched_remote_names) {
-		advise(_("  %s"), item->string);
-	}
-	advise(_("If you meant to create a worktree from a remote tracking branch on\n"
-		 "<remote>, you can do so by:\n"
-		 "\n"
-		 "    git worktree add -b %s %s <remote>/%s\n"
-		 "\n"
-		 "If you'd like to always prefer some remote, e.g. 'origin',\n"
-		 "consider setting checkout.defaultRemote=origin in your config."),
-	       branch, path, branch);
-}
-
 static int add(int ac, const char **av, const char *prefix,
 	       struct repository *repo UNUSED)
 {
@@ -909,7 +923,7 @@ static int add(int ac, const char **av, const char *prefix,
 		opts.orphan = dwim_orphan(&opts, !!opt_track, 0);
 	} else if (ac < 2) {
 		/* DWIM: Guess branch name from path. */
-		char *s = dwim_branch(path, &new_branch_to_free);
+		char *s = dwim_branch(&opts, path, &new_branch_to_free);
 		if (s)
 			branch = branch_to_free = s;
 		new_branch = new_branch_to_free;
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 5c105cf252..a37137042d 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -669,6 +669,19 @@ test_expect_success 'git worktree add --guess-remote sets up tracking' '
 		test_cmp_rev refs/remotes/repo_a/foo refs/heads/foo
 	)
 '
+
+test_expect_success 'git worktree add --guess-remote fails if there are multiple matches' '
+	test_when_finished rm -rf repo_a repo_b foo &&
+	setup_remote_repo repo_a repo_b &&
+	(
+		cd repo_b &&
+		git remote add repo_a2 ../repo_a &&
+		git fetch repo_a2 &&
+		test_must_fail git worktree add --guess-remote ../foo 2>actual &&
+		test_grep "matched multiple (2) remote tracking branches" actual
+	)
+'
+
 test_expect_success 'git worktree add --guess-remote sets up tracking (quiet)' '
 	test_when_finished rm -rf repo_a repo_b foo &&
 	setup_remote_repo repo_a repo_b &&

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 55e3a89a85..650eda735f 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1343,6 +1343,34 @@ enum checkout_command {
 	CHECKOUT_RESTORE = 3,
 };
 
+static void advice_disambiguating_remotes(enum checkout_command which_command)
+{
+	const char *cmdname;
+
+	switch (which_command) {
+	case CHECKOUT_CHECKOUT:
+		cmdname = "checkout";
+		break;
+	case CHECKOUT_SWITCH:
+		cmdname = "switch";
+		break;
+	default:
+		BUG("command <%d> should not reach parse_remote_branch",
+		    which_command);
+		break;
+	}
+
+	advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+		 "you can do so by fully qualifying the name with the --track option:\n"
+		 "\n"
+		 "    git %s --track origin/<name>\n"
+		 "\n"
+		 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+		 "one remote, e.g. the 'origin' remote, consider setting\n"
+		 "checkout.defaultRemote=origin in your config."),
+	       cmdname);
+}
+
 static char *parse_remote_branch(const char *arg,
 				 struct object_id *rev,
 				 int could_be_checkout_paths,
@@ -1358,35 +1386,11 @@ static char *parse_remote_branch(const char *arg,
 	}
 
 	if (!remote && num_matches > 1) {
-	    if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME)) {
-		    const char *cmdname;
-
-		    switch (which_command) {
-		    case CHECKOUT_CHECKOUT:
-			    cmdname = "checkout";
-			    break;
-		    case CHECKOUT_SWITCH:
-			    cmdname = "switch";
-			    break;
-		    default:
-			    BUG("command <%d> should not reach parse_remote_branch",
-				which_command);
-			    break;
-		    }
-
-		    advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
-			     "you can do so by fully qualifying the name with the --track option:\n"
-			     "\n"
-			     "    git %s --track origin/<name>\n"
-			     "\n"
-			     "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
-			     "one remote, e.g. the 'origin' remote, consider setting\n"
-			     "checkout.defaultRemote=origin in your config."),
-			   cmdname);
-	    }
-
-	    die(_("'%s' matched multiple (%d) remote tracking branches"),
-		arg, num_matches);
+		if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+			advice_disambiguating_remotes(which_command);
+
+		die(_("'%s' matched multiple (%d) remote tracking branches"),
+		    arg, num_matches);
 	}
 
 	return remote;

builtin/checkout.c, builtin/worktree.c, checkout.c, checkout.h

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 650eda735f..07373615d8 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1343,9 +1343,12 @@ enum checkout_command {
 	CHECKOUT_RESTORE = 3,
 };
 
-static void advice_disambiguating_remotes(enum checkout_command which_command)
+static void advise_disambiguating_remotes(enum checkout_command which_command,
+					  const char *branch,
+					  const struct string_list *matched_remote_names)
 {
 	const char *cmdname;
+	struct string_list_item *item;
 
 	switch (which_command) {
 	case CHECKOUT_CHECKOUT:
@@ -1360,15 +1363,19 @@ static void advice_disambiguating_remotes(enum checkout_command which_command)
 		break;
 	}
 
-	advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+	advise(_("Branch name '%s' appears in multiple remotes:"), branch);
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to check out a remote tracking branch on <remote>,\n"
 		 "you can do so by fully qualifying the name with the --track option:\n"
 		 "\n"
-		 "    git %s --track origin/<name>\n"
+		 "    git %s --track <remote>/%s\n"
 		 "\n"
-		 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+		 "If you'd like to always have checkouts of an ambiguous name prefer\n"
 		 "one remote, e.g. the 'origin' remote, consider setting\n"
 		 "checkout.defaultRemote=origin in your config."),
-	       cmdname);
+	       cmdname, branch);
 }
 
 static char *parse_remote_branch(const char *arg,
@@ -1377,7 +1384,10 @@ static char *parse_remote_branch(const char *arg,
 				 enum checkout_command which_command)
 {
 	int num_matches = 0;
-	char *remote = unique_tracking_name(arg, rev, &num_matches);
+	struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+	char *remote = unique_tracking_name(arg, rev, &num_matches,
+					    &matched_remote_names);
 
 	if (remote && could_be_checkout_paths) {
 		die(_("'%s' could be both a local file and a tracking branch.\n"
@@ -1387,12 +1397,14 @@ static char *parse_remote_branch(const char *arg,
 
 	if (!remote && num_matches > 1) {
 		if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
-			advice_disambiguating_remotes(which_command);
-
+			advise_disambiguating_remotes(which_command, arg,
+						      &matched_remote_names);
 		die(_("'%s' matched multiple (%d) remote tracking branches"),
 		    arg, num_matches);
 	}
 
+	string_list_clear(&matched_remote_names, 0);
+
 	return remote;
 }
 
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 654d27c3e1..22c8e5e131 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -782,7 +782,7 @@ static char *dwim_branch(const char *path, char **new_branch)
 	*new_branch = branchname;
 	if (guess_remote) {
 		struct object_id oid;
-		char *remote = unique_tracking_name(*new_branch, &oid, NULL);
+		char *remote = unique_tracking_name(*new_branch, &oid, NULL, NULL);
 		return remote;
 	}
 	return NULL;
@@ -904,7 +904,7 @@ static int add(int ac, const char **av, const char *prefix,
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL);
+			remote = unique_tracking_name(branch, &oid, NULL, NULL);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
diff --git a/checkout.c b/checkout.c
index 1588b116ee..2806b783ec 100644
--- a/checkout.c
+++ b/checkout.c
@@ -8,6 +8,7 @@
 #include "checkout.h"
 #include "config.h"
 #include "strbuf.h"
+#include "string-list.h"
 
 struct tracking_name_data {
 	/* const */ char *src_ref;
@@ -17,6 +18,7 @@ struct tracking_name_data {
 	const char *default_remote;
 	char *default_dst_ref;
 	struct object_id *default_dst_oid;
+	struct string_list **remote_names;
 };
 
 #define TRACKING_NAME_DATA_INIT { 0 }
@@ -39,6 +41,8 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 		oidcpy(dst, cb->dst_oid);
 		cb->default_dst_oid = dst;
 	}
+	if (cb->remote_names)
+		string_list_append(*cb->remote_names, remote->name);
 	if (cb->dst_ref) {
 		free(query.dst);
 		return 0;
@@ -48,14 +52,20 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 }
 
 char *unique_tracking_name(const char *name, struct object_id *oid,
-			   int *dwim_remotes_matched)
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names)
 {
 	struct tracking_name_data cb_data = TRACKING_NAME_DATA_INIT;
 	const char *default_remote = NULL;
-	if (!repo_config_get_string_tmp(the_repository, "checkout.defaultremote", &default_remote))
+
+	if (!repo_config_get_string_tmp(the_repository,
+					"checkout.defaultremote",
+					&default_remote))
 		cb_data.default_remote = default_remote;
 	cb_data.src_ref = xstrfmt("refs/heads/%s", name);
 	cb_data.dst_oid = oid;
+	if (dwim_remote_names)
+		cb_data.remote_names = &dwim_remote_names;
 	for_each_remote(check_tracking_name, &cb_data);
 	if (dwim_remotes_matched)
 		*dwim_remotes_matched = cb_data.num_matches;
diff --git a/checkout.h b/checkout.h
index 55920e7aeb..0b185a0fc9 100644
--- a/checkout.h
+++ b/checkout.h
@@ -3,6 +3,8 @@
 
 #include "hash.h"
 
+struct string_list;
+
 /*
  * Check if the branch name uniquely matches a branch name on a remote
  * tracking branch.  Return the name of the remote if such a branch
@@ -10,6 +12,7 @@
  */
 char *unique_tracking_name(const char *name,
 			   struct object_id *oid,
-			   int *dwim_remotes_matched);
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names);
 
 #endif /* CHECKOUT_H */

builtin/worktree.c, t/t2400-worktree-add.sh

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 22c8e5e131..c745deddde 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -764,6 +764,25 @@ static int dwim_orphan(const struct add_opts *opts, int opt_track, int remote)
 	return 1;
 }
 
+static void advise_disambiguating_remotes(const char *path, const char *branch,
+					  const struct string_list *matched_remote_names)
+{
+	struct string_list_item *item;
+
+	advise(_("Branch name '%s' appears in multiple remotes:"), branch);
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to create a worktree from a remote tracking branch on\n"
+		 "<remote>, you can do so by:\n"
+		 "\n"
+		 "    git worktree add -b %s %s <remote>/%s\n"
+		 "\n"
+		 "If you'd like to always prefer some remote, e.g. 'origin',\n"
+		 "consider setting checkout.defaultRemote=origin in your config."),
+	       branch, path, branch);
+}
+
 static char *dwim_branch(const char *path, char **new_branch)
 {
 	int n;
@@ -898,17 +917,29 @@ static int add(int ac, const char **av, const char *prefix,
 		/* DWIM: Infer --orphan when repo has no refs. */
 		opts.orphan = (!s) && dwim_orphan(&opts, !!opt_track, 1);
 	} else if (ac == 2) {
-		struct object_id oid;
 		struct commit *commit;
-		char *remote;
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL, NULL);
+			struct object_id oid;
+			char *remote;
+			int num_matches = 0;
+			struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+			remote = unique_tracking_name(branch, &oid, &num_matches,
+						      &matched_remote_names);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
+			} else if (num_matches > 1) {
+				if (!opts.quiet &&
+				    advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+					advise_disambiguating_remotes(path, branch,
+								      &matched_remote_names);
+				die(_("'%s' matched multiple (%d) remote tracking branches"),
+				    branch, num_matches);
 			}
+			string_list_clear(&matched_remote_names, 0);
 		}
 
 		if (!strcmp(branch, "HEAD"))
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 87b926728a..5c105cf252 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -624,12 +624,12 @@ test_expect_success '"add" <path> <branch> dwims' '
 test_expect_success '"add" <path> <branch> dwims with checkout.defaultRemote' '
 	test_when_finished rm -rf repo_upstream repo_dwim foo &&
 	setup_remote_repo repo_upstream repo_dwim &&
-	git init repo_dwim &&
 	(
 		cd repo_dwim &&
 		git remote add repo_upstream2 ../repo_upstream &&
 		git fetch repo_upstream2 &&
-		test_must_fail git worktree add ../foo foo &&
+		test_must_fail git worktree add ../foo foo 2>error.actual &&
+		test_grep "matched multiple (2) remote tracking branches" error.actual &&
 		git -c checkout.defaultRemote=repo_upstream worktree add ../foo foo &&
 		git status -uno --porcelain >status.actual &&
 		test_must_be_empty status.actual

Documentation/config/worktree.adoc, Documentation/git-worktree.adoc, builtin/worktree.c, t/t2400-worktree-add.sh

diff --git a/Documentation/config/worktree.adoc b/Documentation/config/worktree.adoc
index a248076ea5..0930183b91 100644
--- a/Documentation/config/worktree.adoc
+++ b/Documentation/config/worktree.adoc
@@ -5,8 +5,9 @@
 	set to true, `worktree add` tries to find a remote-tracking
 	branch whose name uniquely matches the new branch name.  If
 	such a branch exists, it is checked out and set as "upstream"
-	for the new branch.  If no such match can be found, it falls
-	back to creating a new branch from the current `HEAD`.
+	for the new branch.  If multiple matches are found, the command
+	fails.  If no such match can be found, it falls back to
+	creating a new branch from the current `HEAD`.
 
 `worktree.useRelativePaths`::
 	Link worktrees using relative paths (when "`true`") or absolute
diff --git a/Documentation/git-worktree.adoc b/Documentation/git-worktree.adoc
index fbf8426cd9..32787eacc3 100644
--- a/Documentation/git-worktree.adoc
+++ b/Documentation/git-worktree.adoc
@@ -219,7 +219,9 @@ To remove a locked worktree, specify `--force` twice.
 	of creating a new branch from `HEAD`, if there exists a tracking
 	branch in exactly one remote matching the basename of _<path>_,
 	base the new branch on the remote-tracking branch, and mark
-	the remote-tracking branch as "upstream" from the new branch.
+	the remote-tracking branch as "upstream" from the new branch. If
+	there are multiple matches, the command fails. If there is no
+	match, the command falls back to creating a new branch from `HEAD`.
 +
 This can also be set up as the default behaviour by using the
 `worktree.guessRemote` config option.
diff --git a/builtin/worktree.c b/builtin/worktree.c
index c745deddde..07163bf9b7 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -783,7 +783,7 @@ static void advise_disambiguating_remotes(const char *path, const char *branch,
 	       branch, path, branch);
 }
 
-static char *dwim_branch(const char *path, char **new_branch)
+static char *dwim_branch(const struct add_opts *opts, const char *path, char **new_branch)
 {
 	int n;
 	int branch_exists;
@@ -801,7 +801,21 @@ static char *dwim_branch(const char *path, char **new_branch)
 	*new_branch = branchname;
 	if (guess_remote) {
 		struct object_id oid;
-		char *remote = unique_tracking_name(*new_branch, &oid, NULL, NULL);
+		char *remote;
+		int num_matches = 0;
+		struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+		remote = unique_tracking_name(*new_branch, &oid, &num_matches,
+					      &matched_remote_names);
+		if (!remote && num_matches > 1) {
+			if (!opts->quiet &&
+			    advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+				advise_disambiguating_remotes(path, *new_branch,
+							      &matched_remote_names);
+			die(_("'%s' matched multiple (%d) remote tracking branches"),
+			    *new_branch, num_matches);
+		}
+		string_list_clear(&matched_remote_names, 0);
 		return remote;
 	}
 	return NULL;
@@ -909,7 +923,7 @@ static int add(int ac, const char **av, const char *prefix,
 		opts.orphan = dwim_orphan(&opts, !!opt_track, 0);
 	} else if (ac < 2) {
 		/* DWIM: Guess branch name from path. */
-		char *s = dwim_branch(path, &new_branch_to_free);
+		char *s = dwim_branch(&opts, path, &new_branch_to_free);
 		if (s)
 			branch = branch_to_free = s;
 		new_branch = new_branch_to_free;
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 5c105cf252..a37137042d 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -669,6 +669,19 @@ test_expect_success 'git worktree add --guess-remote sets up tracking' '
 		test_cmp_rev refs/remotes/repo_a/foo refs/heads/foo
 	)
 '
+
+test_expect_success 'git worktree add --guess-remote fails if there are multiple matches' '
+	test_when_finished rm -rf repo_a repo_b foo &&
+	setup_remote_repo repo_a repo_b &&
+	(
+		cd repo_b &&
+		git remote add repo_a2 ../repo_a &&
+		git fetch repo_a2 &&
+		test_must_fail git worktree add --guess-remote ../foo 2>actual &&
+		test_grep "matched multiple (2) remote tracking branches" actual
+	)
+'
+
 test_expect_success 'git worktree add --guess-remote sets up tracking (quiet)' '
 	test_when_finished rm -rf repo_a repo_b foo &&
 	setup_remote_repo repo_a repo_b &&

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 55e3a89a85..3cd5fff709 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1343,6 +1343,34 @@ enum checkout_command {
 	CHECKOUT_RESTORE = 3,
 };
 
+static void advise_disambiguating_remotes(enum checkout_command which_command)
+{
+	const char *cmdname;
+
+	switch (which_command) {
+	case CHECKOUT_CHECKOUT:
+		cmdname = "checkout";
+		break;
+	case CHECKOUT_SWITCH:
+		cmdname = "switch";
+		break;
+	default:
+		BUG("command <%d> should not reach advise_disambiguating_remotes",
+		    which_command);
+		break;
+	}
+
+	advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+		 "you can do so by fully qualifying the name with the --track option:\n"
+		 "\n"
+		 "    git %s --track origin/<name>\n"
+		 "\n"
+		 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+		 "one remote, e.g. the 'origin' remote, consider setting\n"
+		 "checkout.defaultRemote=origin in your config."),
+	       cmdname);
+}
+
 static char *parse_remote_branch(const char *arg,
 				 struct object_id *rev,
 				 int could_be_checkout_paths,
@@ -1358,35 +1386,11 @@ static char *parse_remote_branch(const char *arg,
 	}
 
 	if (!remote && num_matches > 1) {
-	    if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME)) {
-		    const char *cmdname;
-
-		    switch (which_command) {
-		    case CHECKOUT_CHECKOUT:
-			    cmdname = "checkout";
-			    break;
-		    case CHECKOUT_SWITCH:
-			    cmdname = "switch";
-			    break;
-		    default:
-			    BUG("command <%d> should not reach parse_remote_branch",
-				which_command);
-			    break;
-		    }
-
-		    advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
-			     "you can do so by fully qualifying the name with the --track option:\n"
-			     "\n"
-			     "    git %s --track origin/<name>\n"
-			     "\n"
-			     "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
-			     "one remote, e.g. the 'origin' remote, consider setting\n"
-			     "checkout.defaultRemote=origin in your config."),
-			   cmdname);
-	    }
-
-	    die(_("'%s' matched multiple (%d) remote tracking branches"),
-		arg, num_matches);
+		if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+			advise_disambiguating_remotes(which_command);
+
+		die(_("'%s' matched multiple (%d) remote tracking branches"),
+		    arg, num_matches);
 	}
 
 	return remote;

builtin/checkout.c, builtin/worktree.c, checkout.c, checkout.h

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 3cd5fff709..2bc21aa49b 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1343,9 +1343,12 @@ enum checkout_command {
 	CHECKOUT_RESTORE = 3,
 };
 
-static void advise_disambiguating_remotes(enum checkout_command which_command)
+static void advise_disambiguating_remotes(enum checkout_command which_command,
+					  const char *branch,
+					  const struct string_list *matched_remote_names)
 {
 	const char *cmdname;
+	struct string_list_item *item;
 
 	switch (which_command) {
 	case CHECKOUT_CHECKOUT:
@@ -1360,15 +1363,19 @@ static void advise_disambiguating_remotes(enum checkout_command which_command)
 		break;
 	}
 
-	advise(_("If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+	advise(_("Branch name '%s' appears in multiple remotes:"), branch);
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to check out a remote tracking branch on <remote>,\n"
 		 "you can do so by fully qualifying the name with the --track option:\n"
 		 "\n"
-		 "    git %s --track origin/<name>\n"
+		 "    git %s --track <remote>/%s\n"
 		 "\n"
-		 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+		 "If you'd like to always have checkouts of an ambiguous name prefer\n"
 		 "one remote, e.g. the 'origin' remote, consider setting\n"
 		 "checkout.defaultRemote=origin in your config."),
-	       cmdname);
+	       cmdname, branch);
 }
 
 static char *parse_remote_branch(const char *arg,
@@ -1377,7 +1384,10 @@ static char *parse_remote_branch(const char *arg,
 				 enum checkout_command which_command)
 {
 	int num_matches = 0;
-	char *remote = unique_tracking_name(arg, rev, &num_matches);
+	struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+	char *remote = unique_tracking_name(arg, rev, &num_matches,
+					    &matched_remote_names);
 
 	if (remote && could_be_checkout_paths) {
 		die(_("'%s' could be both a local file and a tracking branch.\n"
@@ -1387,12 +1397,14 @@ static char *parse_remote_branch(const char *arg,
 
 	if (!remote && num_matches > 1) {
 		if (advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
-			advise_disambiguating_remotes(which_command);
-
+			advise_disambiguating_remotes(which_command, arg,
+						      &matched_remote_names);
 		die(_("'%s' matched multiple (%d) remote tracking branches"),
 		    arg, num_matches);
 	}
 
+	string_list_clear(&matched_remote_names, 0);
+
 	return remote;
 }
 
diff --git a/builtin/worktree.c b/builtin/worktree.c
index 654d27c3e1..22c8e5e131 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -782,7 +782,7 @@ static char *dwim_branch(const char *path, char **new_branch)
 	*new_branch = branchname;
 	if (guess_remote) {
 		struct object_id oid;
-		char *remote = unique_tracking_name(*new_branch, &oid, NULL);
+		char *remote = unique_tracking_name(*new_branch, &oid, NULL, NULL);
 		return remote;
 	}
 	return NULL;
@@ -904,7 +904,7 @@ static int add(int ac, const char **av, const char *prefix,
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL);
+			remote = unique_tracking_name(branch, &oid, NULL, NULL);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
diff --git a/checkout.c b/checkout.c
index 1588b116ee..a0d0229435 100644
--- a/checkout.c
+++ b/checkout.c
@@ -8,6 +8,7 @@
 #include "checkout.h"
 #include "config.h"
 #include "strbuf.h"
+#include "string-list.h"
 
 struct tracking_name_data {
 	/* const */ char *src_ref;
@@ -17,6 +18,7 @@ struct tracking_name_data {
 	const char *default_remote;
 	char *default_dst_ref;
 	struct object_id *default_dst_oid;
+	struct string_list *remote_names;
 };
 
 #define TRACKING_NAME_DATA_INIT { 0 }
@@ -39,6 +41,8 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 		oidcpy(dst, cb->dst_oid);
 		cb->default_dst_oid = dst;
 	}
+	if (cb->remote_names)
+		string_list_append(cb->remote_names, remote->name);
 	if (cb->dst_ref) {
 		free(query.dst);
 		return 0;
@@ -48,14 +52,19 @@ static int check_tracking_name(struct remote *remote, void *cb_data)
 }
 
 char *unique_tracking_name(const char *name, struct object_id *oid,
-			   int *dwim_remotes_matched)
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names)
 {
 	struct tracking_name_data cb_data = TRACKING_NAME_DATA_INIT;
 	const char *default_remote = NULL;
-	if (!repo_config_get_string_tmp(the_repository, "checkout.defaultremote", &default_remote))
+
+	if (!repo_config_get_string_tmp(the_repository,
+					"checkout.defaultremote",
+					&default_remote))
 		cb_data.default_remote = default_remote;
 	cb_data.src_ref = xstrfmt("refs/heads/%s", name);
 	cb_data.dst_oid = oid;
+	cb_data.remote_names = dwim_remote_names;
 	for_each_remote(check_tracking_name, &cb_data);
 	if (dwim_remotes_matched)
 		*dwim_remotes_matched = cb_data.num_matches;
diff --git a/checkout.h b/checkout.h
index 55920e7aeb..0b185a0fc9 100644
--- a/checkout.h
+++ b/checkout.h
@@ -3,6 +3,8 @@
 
 #include "hash.h"
 
+struct string_list;
+
 /*
  * Check if the branch name uniquely matches a branch name on a remote
  * tracking branch.  Return the name of the remote if such a branch
@@ -10,6 +12,7 @@
  */
 char *unique_tracking_name(const char *name,
 			   struct object_id *oid,
-			   int *dwim_remotes_matched);
+			   int *dwim_remotes_matched,
+			   struct string_list *dwim_remote_names);
 
 #endif /* CHECKOUT_H */

builtin/worktree.c, t/t2400-worktree-add.sh

diff --git a/builtin/worktree.c b/builtin/worktree.c
index 22c8e5e131..c745deddde 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -764,6 +764,25 @@ static int dwim_orphan(const struct add_opts *opts, int opt_track, int remote)
 	return 1;
 }
 
+static void advise_disambiguating_remotes(const char *path, const char *branch,
+					  const struct string_list *matched_remote_names)
+{
+	struct string_list_item *item;
+
+	advise(_("Branch name '%s' appears in multiple remotes:"), branch);
+	for_each_string_list_item(item, matched_remote_names) {
+		advise(_("  %s"), item->string);
+	}
+	advise(_("If you meant to create a worktree from a remote tracking branch on\n"
+		 "<remote>, you can do so by:\n"
+		 "\n"
+		 "    git worktree add -b %s %s <remote>/%s\n"
+		 "\n"
+		 "If you'd like to always prefer some remote, e.g. 'origin',\n"
+		 "consider setting checkout.defaultRemote=origin in your config."),
+	       branch, path, branch);
+}
+
 static char *dwim_branch(const char *path, char **new_branch)
 {
 	int n;
@@ -898,17 +917,29 @@ static int add(int ac, const char **av, const char *prefix,
 		/* DWIM: Infer --orphan when repo has no refs. */
 		opts.orphan = (!s) && dwim_orphan(&opts, !!opt_track, 1);
 	} else if (ac == 2) {
-		struct object_id oid;
 		struct commit *commit;
-		char *remote;
 
 		commit = lookup_commit_reference_by_name(branch);
 		if (!commit) {
-			remote = unique_tracking_name(branch, &oid, NULL, NULL);
+			struct object_id oid;
+			char *remote;
+			int num_matches = 0;
+			struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+			remote = unique_tracking_name(branch, &oid, &num_matches,
+						      &matched_remote_names);
 			if (remote) {
 				new_branch = branch;
 				branch = new_branch_to_free = remote;
+			} else if (num_matches > 1) {
+				if (!opts.quiet &&
+				    advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+					advise_disambiguating_remotes(path, branch,
+								      &matched_remote_names);
+				die(_("'%s' matched multiple (%d) remote tracking branches"),
+				    branch, num_matches);
 			}
+			string_list_clear(&matched_remote_names, 0);
 		}
 
 		if (!strcmp(branch, "HEAD"))
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 87b926728a..5c105cf252 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -624,12 +624,12 @@ test_expect_success '"add" <path> <branch> dwims' '
 test_expect_success '"add" <path> <branch> dwims with checkout.defaultRemote' '
 	test_when_finished rm -rf repo_upstream repo_dwim foo &&
 	setup_remote_repo repo_upstream repo_dwim &&
-	git init repo_dwim &&
 	(
 		cd repo_dwim &&
 		git remote add repo_upstream2 ../repo_upstream &&
 		git fetch repo_upstream2 &&
-		test_must_fail git worktree add ../foo foo &&
+		test_must_fail git worktree add ../foo foo 2>error.actual &&
+		test_grep "matched multiple (2) remote tracking branches" error.actual &&
 		git -c checkout.defaultRemote=repo_upstream worktree add ../foo foo &&
 		git status -uno --porcelain >status.actual &&
 		test_must_be_empty status.actual

Documentation/config/worktree.adoc, Documentation/git-worktree.adoc, builtin/worktree.c, t/t2400-worktree-add.sh

diff --git a/Documentation/config/worktree.adoc b/Documentation/config/worktree.adoc
index a248076ea5..0930183b91 100644
--- a/Documentation/config/worktree.adoc
+++ b/Documentation/config/worktree.adoc
@@ -5,8 +5,9 @@
 	set to true, `worktree add` tries to find a remote-tracking
 	branch whose name uniquely matches the new branch name.  If
 	such a branch exists, it is checked out and set as "upstream"
-	for the new branch.  If no such match can be found, it falls
-	back to creating a new branch from the current `HEAD`.
+	for the new branch.  If multiple matches are found, the command
+	fails.  If no such match can be found, it falls back to
+	creating a new branch from the current `HEAD`.
 
 `worktree.useRelativePaths`::
 	Link worktrees using relative paths (when "`true`") or absolute
diff --git a/Documentation/git-worktree.adoc b/Documentation/git-worktree.adoc
index fbf8426cd9..32787eacc3 100644
--- a/Documentation/git-worktree.adoc
+++ b/Documentation/git-worktree.adoc
@@ -219,7 +219,9 @@ To remove a locked worktree, specify `--force` twice.
 	of creating a new branch from `HEAD`, if there exists a tracking
 	branch in exactly one remote matching the basename of _<path>_,
 	base the new branch on the remote-tracking branch, and mark
-	the remote-tracking branch as "upstream" from the new branch.
+	the remote-tracking branch as "upstream" from the new branch. If
+	there are multiple matches, the command fails. If there is no
+	match, the command falls back to creating a new branch from `HEAD`.
 +
 This can also be set up as the default behaviour by using the
 `worktree.guessRemote` config option.
diff --git a/builtin/worktree.c b/builtin/worktree.c
index c745deddde..07163bf9b7 100644
--- a/builtin/worktree.c
+++ b/builtin/worktree.c
@@ -783,7 +783,7 @@ static void advise_disambiguating_remotes(const char *path, const char *branch,
 	       branch, path, branch);
 }
 
-static char *dwim_branch(const char *path, char **new_branch)
+static char *dwim_branch(const struct add_opts *opts, const char *path, char **new_branch)
 {
 	int n;
 	int branch_exists;
@@ -801,7 +801,21 @@ static char *dwim_branch(const char *path, char **new_branch)
 	*new_branch = branchname;
 	if (guess_remote) {
 		struct object_id oid;
-		char *remote = unique_tracking_name(*new_branch, &oid, NULL, NULL);
+		char *remote;
+		int num_matches = 0;
+		struct string_list matched_remote_names = STRING_LIST_INIT_DUP;
+
+		remote = unique_tracking_name(*new_branch, &oid, &num_matches,
+					      &matched_remote_names);
+		if (!remote && num_matches > 1) {
+			if (!opts->quiet &&
+			    advice_enabled(ADVICE_CHECKOUT_AMBIGUOUS_REMOTE_BRANCH_NAME))
+				advise_disambiguating_remotes(path, *new_branch,
+							      &matched_remote_names);
+			die(_("'%s' matched multiple (%d) remote tracking branches"),
+			    *new_branch, num_matches);
+		}
+		string_list_clear(&matched_remote_names, 0);
 		return remote;
 	}
 	return NULL;
@@ -909,7 +923,7 @@ static int add(int ac, const char **av, const char *prefix,
 		opts.orphan = dwim_orphan(&opts, !!opt_track, 0);
 	} else if (ac < 2) {
 		/* DWIM: Guess branch name from path. */
-		char *s = dwim_branch(path, &new_branch_to_free);
+		char *s = dwim_branch(&opts, path, &new_branch_to_free);
 		if (s)
 			branch = branch_to_free = s;
 		new_branch = new_branch_to_free;
diff --git a/t/t2400-worktree-add.sh b/t/t2400-worktree-add.sh
index 5c105cf252..a37137042d 100755
--- a/t/t2400-worktree-add.sh
+++ b/t/t2400-worktree-add.sh
@@ -669,6 +669,19 @@ test_expect_success 'git worktree add --guess-remote sets up tracking' '
 		test_cmp_rev refs/remotes/repo_a/foo refs/heads/foo
 	)
 '
+
+test_expect_success 'git worktree add --guess-remote fails if there are multiple matches' '
+	test_when_finished rm -rf repo_a repo_b foo &&
+	setup_remote_repo repo_a repo_b &&
+	(
+		cd repo_b &&
+		git remote add repo_a2 ../repo_a &&
+		git fetch repo_a2 &&
+		test_must_fail git worktree add --guess-remote ../foo 2>actual &&
+		test_grep "matched multiple (2) remote tracking branches" actual
+	)
+'
+
 test_expect_success 'git worktree add --guess-remote sets up tracking (quiet)' '
 	test_when_finished rm -rf repo_a repo_b foo &&
 	setup_remote_repo repo_a repo_b &&