Hello, For the default signal combiner last_value, last_value<void>::result_type is currently set to last_value<void>::unusable. On compilers which support void returns, it seems like it would be more beneficial to set it to void instead. I.e., template<> struct last_value<void> { #ifdef BOOST_NO_VOID_RETURNS struct unusable {}; public: typedef unusable result_type; #else public: typedef void result_type; #endif // BOOST_NO_VOID_RETURNS ... I have submitted trac ticket #1043 to this effect with the trivial patch attached, in case this change would be OK. Thanks, Stjepan