https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63219
--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> --- N.B. as a workaround for GCC 4.9.1 you can call the function with an explicit template argument list: std::string fmt = "$1"; m.format<std::char_traits<char>>(fmt); For 4.9.1 the template argument matches the superfluous parameter and so is ignored, for the fixed implementation the template argument is the same type as would be deduced anyway so is redundant but harmless. But it's easier to just do m.format(fmt.c_str()) if you need the code to work with 4.9.1
