There is a config pull request outstanding that includes <boost/predef.h>. If it was almost any library other than config, I'd apply this without a second thought. But Boost config is special in that if it breaks, virtually the whole of boost breaks. So it makes sense to be cautious about dependencies. Has there been any discussion about the relationship between Boost.config and Boost.predef? Even if we accept the patch, is <boost/predef.h> the right header? It just forwards: #include <boost/predef/language.h> #include <boost/predef/architecture.h> #include <boost/predef/compiler.h> #include <boost/predef/library.h> #include <boost/predef/os.h> #include <boost/predef/other.h> #include <boost/predef/platform.h> The rationale for the pull request is a need in other Boost libraries to detect Windows platform variants like BOOST_PLAT_WINDOWS_DESKTOP andBOOST_PLAT_WINDOWS_RUNTIME. Boost.Predef does a nice job of that. But the only header strictly needed is <boost/predef/platform.h>. So the desired effect can be achieved several ways: 1) #include <boost/predef.h> in the include/boost/config/platform/ headers. 2) #include <boost/predef/platform.h> in the include/boost/config/platform/ headers. 3) #include <boost/predef.h> in the files that actually use the desired macros. 4) #include <boost/predef/platform.h> in the files that actually use the desired macros. If I had been writing the code myself, I probably would have selected option (4). What do others think? --Beman