The following test code (inside #if 1) generates a LNK2019 (unresolved external symbol) with 1.70.0 but links successfully with 1.69.0. Inspecting read_until.hpp, I suspect the problem is with the enable_if expansion being too complex for the older compiler. (Hence the #if0 code which tests the individual conditions, but those seem to work fine.) The same code links with VS2019 and VS2015, and this linked under the previous Boost with VS2010. int _tmain(int argc, _TCHAR* argv[]) { typedef boost::asio::streambuf buftype; #if 0 const bool v1 = boost::asio::is_dynamic_buffer_v1::value; const bool notv2 = !boost::asio::is_dynamic_buffer_v2::value; #endif #if 0 void* cond = boost::enable_if< boost::asio::is_dynamic_buffer_v1::value && !boost::asio::is_dynamic_buffer_v2::value >::type* 0; #endif #if 1 boost::asio::io_service ios; boost::asio::ip::tcp::socket socket(ios); boost::asio::streambuf buf; boost::asio::async_read_until(socket, buf, '\n', NULL); #endif return 0; }