Hi, We just stumbled across a small problem with Boost.Signals, while playing with the symbol visibility features of gcc-3.4 and gcc-4. That feature is still buggy, but it unveiled some strange code. Somehow gcc failed to turn the type info of the types stored by any into a visible symbol, which is required for using boost::signals across shared libraries. So there are multiple type info objects and the dynamic_casts within signal failed, and the application crashed with a seg fault, since no one expected the cast to fail The code is in signal_template.hpp: template<typename Pair> R operator()(const Pair& slot) const { F* target = const_cast<F*>(any_cast<F>(&slot.second)); return (*target)(BOOST_SIGNALS_BOUND_ARGS); } I dont see why any_cast is used here at all. The type safety is guranteed by the interface of Boost.Signals, so I doubt that someone will be able to abuse the library. I believe the author of that code had the same in mind, since he did not test target != 0 before invoking the target. So in my opinion a simple reinterpret_cast should suffice here. It would also fix our issue, although that one is caused by gcc. Regards Andreas Pokorny