How to fix “Your branch and 'origin/master' have diverged” after editing a commit that came before a pull?

In the following scenario:

1. Make commits A, B, C
2. Pull, getting commits D, E
3. Make more commits F, G, H, ...
4. Realize that you need to tweak B
5. Tweak B using git rebase -i and git commit --amend

Now git status says:

  Your branch and 'origin/master' have diverged.

How should I fix this? Thanks.