https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122053
--- Comment #4 from Nathaniel Shead <nshead at gcc dot gnu.org> --- Yeah, currently the only safe way to do it is to have all module imports after any #includes; MSVC and Clang (albeit to a lesser degree) have similar issues and recommendations so most people that I've seen with modules projects follow suit.