https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107402
--- Comment #2 from Andrey Bolshakov <bolsh.andrey at yandex dot ru> --- I would say that the wording forbids any parenthesized reference initialization with more than one argument, even when there is a corresponding constructor. E.g., for: struct C { C(int, int); }; GCC wrongly (I think) evaluates __is_constructible(C&&, int, int) to true, despite it rejects const C& ref(1, 1); for some reason.