When compiling using /fpermissive- (enable strict conformance) I get the following compilation error: boost\boost\range\concepts.hpp(257): error C3646: 'n': unknown override specifier boost\boost\range\concepts.hpp(264): note: see reference to class template instantiation 'boost::range_detail::RandomAccessIteratorConcept<Iterator>' being compiled boost\libs\beast\include\boost\beast\core\string.hpp(87): note: see reference to class template instantiation 'boost::basic_string_view<char,std::char_traits<char>>' being compiled boost\boost\range\concepts.hpp(257): error C4430: missing type specifier - int assumed. Note: C++ does not support default-int boost\boost\range\concepts.hpp(257): error C3646: 'n': unknown override specifier boost\boost\range\concepts.hpp(264): note: see reference to class template instantiation 'boost::range_detail::RandomAccessIteratorConcept<Iterator>' being compiled I'm using the tip of master, digest 000bd8507f8a17ada2c1fef19158e16cdeabd631 Thanks