Forward declaration of enum iterator_selection?

When refs.c is being compiled, the only mention of enum iterator_selection is in this piece of code pulled in from refs-internal.h (have a look at the preprocessed code):

typedef enum iterator_selection ref_iterator_select_fn(
		struct ref_iterator *iter0, struct ref_iterator *iter1,
		void *cb_data);

This looks like a forward declarations of an enumeration type name, something that I thought is illegal in C. Am I wrong? (That may well be the case, my C-foo is quite rusty.)

My compiler does not complain (it's gcc 4.8), but I thought I mention it before someone with a pickier compiler stumbles over it...

-- Hannes