There appears to be two predefined macro spelling mistakes in signals2/detail/variadic_slot_invoker.hpp. It says _MSVC_VER where it should say _MSC_VER. #if defined(_MSVC_VER) // <-- Here # pragma warning(push) # pragma warning(disable:4100) // unreferenced formal parameter #endif ... #if defined(_MSVC_VER) // <-- ... and here # pragma warning(pop) #endif Regards, Anders Dalvander