[Boost-users] [type_erasure] BOOST_TYPE_ERASURE_MEMBER within namespace?

I find that using BOOST_TYPE_ERASURE_MEMBER within my own namespace fails with compilation errors: myprog.cpp:23:1: error: no template named 'concept_interface'; did you mean '::boost::type_erasure::concept_interface'? This is with Boost 1.57, compiled with Apple clang from Xcode 7.1.1. Moving BOOST_TYPE_ERASURE_MEMBER to the global namespace allows successful compilation. I would rather avoid putting my has_member names into the global namespace. How to achieve that?