https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85176
--- Comment #5 from Martin Liška <marxin at gcc dot gnu.org> --- A valid test-case started to find in r251220: $ cat ice.ii namespace a { template <typename b, typename = b> class c; template <typename b, typename d> void e(c<b, d> &); void operator<<(c<char> &f, const char *) { e(f); } extern c<char> cout; } // namespace a int main() { a::cout << ""; }