I ran into an odd error with 1.51.0 when compiling the following code using gcc 4.4.6 on rhel6/64 with -fkeep-inline-functions (using this flag for debug builds): #include int main(void) { boost::filesystem::path a_path; return 0; } The linker complains about an undefined reference to boost::hash_range<> referenced from boost/filesystem/path.hpp. Looking at path.hpp I can see it includes hash_fwd.hpp not hash.hpp. This is despite the fact that it's actually using various hash methods inside the header file (including hash_range). When I change it to use hash.hpp instead, the linker error goes away. Should path.hpp really use hash.hpp instead, or is this some weird compiler issue, or something else entirely? I figured someone here would know =) Thanks, -Mike