id summary reporter owner description type status milestone component version severity resolution keywords cc 12027 is_base_of should work ehen B is incomplete akrzemi1 John Maddock "The Standard ([meta.rel]) requires that in is_base_of D must be a complete type, but it does not require the same of B. This makes sense, because if we compare a complete type D and an incomplete type B, the former is surely not derived from the latter. In contrast, boost::is_base_of imposes an additional constraint that B must also be complete: http://www.boost.org/doc/libs/1_60_0/libs/type_traits/doc/html/boost_typetraits/reference/is_base_of.html Can you remove this extra constraint? It appears to be spoiling one Boost.Optional tests: http://www.boost.org/development/tests/master/developer/output/oracle-sparc-S2-12-5-cpp11-boost-bin-v2-libs-optional-test-optional_test-test-sun-12-5_cpp11-release-threading-multi.html" Bugs closed To Be Determined type_traits Boost 1.61.0 Problem wontfix