When I have "-Wunused-variable" I get these highly annoying warnings from boost/asio/error.hpp which I'm sure almost everyone has seen: boost_1_60_0/boost/asio/error.hpp:258:45: warning: ‘boost::asio::error::system_category’ defined but not used [-Wunused-variable] static const boost::system::error_category& system_category I don't want to disable the warning but I also don't want the false positives. Thankfully, clang and gcc have this wonderful option "-isystem" which lets you mark include paths as belonging to the system. This prevents warnings from being emitted that the programmer can do nothing about. How can I get Boost.Build to add the Boost library header search paths using "-isystem" so that gcc doesn't report warnings in Boost headers that I cannot do anything about? More detail here: http://stackoverflow.com/questions/1867065/how-to-suppress-gcc-warnings-from... I've played around with <sysinclude> but can't seem to figure it out. Here's my Jamroot (my project builds on its own, without putting it in the Boost tree): https://github.com/vinniefalco/Beast/blob/master/Jamroot#L80 -- Follow me on Github: https://github.com/vinniefalco