https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81486
--- Comment #2 from Vittorio Romeo <vittorio.romeo at outlook dot com> --- Here's a snippet that seems to reproduce this bug, even without an explicit deduction guide: template <typename... Ts> struct foo { template <typename... Us> foo(Us...) { } }; int main() { auto f = foo(); } On godbolt: https://godbolt.org/g/CgqLq5