https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66988
--- Comment #2 from Eric Niebler <eric.niebler at gmail dot com> --- I thought that, too. But this program has the same problem: #include <type_traits> template <template <class> class T, class U> concept bool _Valid = requires { typename T<U>; }; template <class T> using __t = typename T::type; template <class T> struct __has_type : std::false_type { }; template <class T> requires _Valid<__t, T> struct __has_type<T> : std::true_type { }; static_assert(!__has_type<int>(), "");