http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60114
--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> --- -Woverflow is turned on by default, so it doesn't matter if you specify it or not; what matters here is the -Wpedantic (we have a bug about that discrepancy: PR59753). So yeah, expected.
