Ambiguous expansion of a macro means that the expansion results in ambiguous code. This is quite independent of who declared the macro's. Whoever provided the macro's provided macro's which expand to ambiguous code. Perhaps Xcode's (or some other thing you are including) is providing macro definitions for MIN and MAX that result in ambiguous code. In order to find out you would need to find the spot at which the complaint is made, find out what the contents of the macro being complained about it as the time that the complaint is made, and then find out who made that declaration. Jolly good compilers will give you all that information at once in the error message. I have no idea if Xcode is a Jolly Good compiler or not, but it sounds from the question that you are asking that it does not fall into that category and is basically giving you the equivalent of a 1980's style "how?" error message.