libstdcpp3.hpp contains: #if defined(__clang_major__) && ((__clang_major__ < 3) || ((__clang_major__ == 3) && (__clang_minor__ < 7))) // As of clang-3.6, libstdc++ header <atomic> throws up errors with clang: # define BOOST_NO_CXX11_HDR_ATOMIC #endif but in the sibling thread about issues with clang-3.6 and thread sanitizer, SmartPtr has been reported to work with -DBOOST_SP_USE_STD_ATOMIC, which uses <atomic>. The reported g++ version is 4.9.2: g++ (Ubuntu 4.9.2-0ubuntu1~14.04) 4.9.2 and Clang is: Ubuntu clang version 3.6.0-svn225356-1~exp1 (trunk) (based on LLVM 3.6.0)