[boost] type_traits for checking derived type

Hi, some code: template <typename DerivedT> class A { BOOST_STATIC_ASSERT((boost::is_convertible<A<DerivedT>*, B*>::value)); [...] }; class B : public A<B> { }; I want to check if the template parameter really specifies a derived type. But the assert is always false. How can i solve this? bye