This has been changed recently but why? The "Install" docs in 'gcc.gnu.org' however still says : --with-gxx-include-dir=dirname Specify the installation directory for G++ header files. The default is prefix/include/c++/version. Writing 'make install' in gcc-4.3.3 really didn't do this but put the headers into '$prefix/$target/include/c++/$version' ! So they became "target and version dependent" instead of the earlier "version dependent". Only the '$prefix/include/c++/$version/$target' was that target dependent in them... So now one MUST specify the old default if one wants the build to follow the documentation and the old learned convention :(