Folks I don't think the headers rule is working very well at present - it seems to both do too much and too little depending on the context: Too much: If I build the type_traits tests so everything is up to date, and then touch say type_with_alignment.hpp, then in libs/type_traits/test do: bjam add_const_test And for some strange reason bjam thinks there's a dependency on type_with_alignment.hpp from add_const_test, and there really isn't. In fact *every* test seems to be out of date now. Too little: The headers under boost/config/ are included via macros so aren't placed in the dependency graph. I can fix this easily enough in the Boost.Config tests, but ideally this should be fixed at the top level by making everything under boost/config/ a dependency of boost/config.hpp. This is currently causing some Boost.Config tests to fail in the online matrix, I bet there are others as well. Anyone any ideas? Thanks, John.