When compiling boost/libs/filesystem/src/path_posix_windows.cpp on windows, a compilation error occurs because BOOST_WINDOWS is redefined. path_posix_windows.cpp has its own definition of BOOST_WINDOWS but this symbol is also defined in win32.hpp which is included by config.hpp. IMMO the definition of BOOST_WINDOWS should be removed and boost/config.hpp should be included instead. toon PS, how it is possible that the regression tests on windows show success for all filesystem tests is a mistery to me. It does not compile on my machine anyway.