Hi, consider the following simple example struct aligned_type { __declspec(align(16)) float vals[4]; }; BOOST_STATIC_ASSERT((boost::is_convertible<aligned_type , aligned_type >::value)); It fails on MSVC 9.0 with boost 1.43 with the following error type_traits/is_convertible.hpp(254) : error C2719: 'unnamed-parameter': formal parameter with __declspec(align('16')) won't be aligned References won't help either BOOST_STATIC_ASSERT((boost::is_convertible<aligned_type &, aligned_type &>::value)); as it breaks with a similar error type_traits/is_convertible.hpp(263) : error C2718: 'const vec_aligned': actual parameter with __declspec(align('16')) won't be aligned A bug database search did not bring up any relevant matches, so I wonder if that is a new issue or just by design? Best regards, Christoph