https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115798
--- Comment #1 from m.cencora at gmail dot com --- Also this is specific to types exported from GMF, if type is declared directly in named module it works fine, i.e. $ cat base.cpp export module base; export { using int8_t = signed char; } export namespace std { using int8_t = ::int8_t; }