In the mpl bitwise.cpp test there are lines like: MPL_ASSERT_RELATION( (bitor_<_0,_ffffffff>::value), ==, 0xffffffff ); MPL_ASSERT_RELATION( (bitor_<_1,_ffffffff>::value), ==, 0xffffffff ); MPL_ASSERT_RELATION( (bitor_<_8,_ffffffff>::value), ==, 0xffffffff ); Using clang under Windows with the VC++ RTL ( clang-cl ), clang gives an error of: bitwise.cpp(43,25) : error: non-type template argument evaluates to 4294967295, which cannot be narrowed to type 'long' [-Wc++11-narrowing] MPL_ASSERT_RELATION( (bitor_<_0,_ffffffff>::value), ==, 0xffffffff ); for the bitor_<_0,_ffffffff>::value expression part since the assert_relation template takes two 'long's as its values. Is this an actual bug according to the C++11 standard ? I would have thought that an unsigned int value of 0xffffffff would fit into a long as a -1, but it sounds like the new standard is saying that since the value of 4294967295 cannot be encompassed by a long it is an error. if it is an error how should it be fixed in MPL ?