diff --git a/include/boost/config/posix_features.hpp b/include/boost/config/posix_features.hpp
index 18729621..0d3f05f5 100644
--- a/include/boost/config/posix_features.hpp
+++ b/include/boost/config/posix_features.hpp
@@ -13,21 +13,21 @@
 // to the user to do this *before* including any header, although
 // in most cases the compiler will do this for you).
 
-#  if defined(BOOST_HAS_UNISTD_H) && defined(_POSIX_C_SOURCE)
+#  if defined(BOOST_HAS_UNISTD_H)
 #     include <unistd.h>
 
       // XOpen has <nl_types.h>, but is this the correct version check?
-#     if defined(_XOPEN_VERSION) && (_XOPEN_VERSION >= 3) && defined(_XOPEN_SOURCE) && (_XOPEN_SOURCE >= 3)
+#     if defined(_XOPEN_VERSION) && (_XOPEN_VERSION >= 3)
 #        define BOOST_HAS_NL_TYPES_H
 #     endif
 
       // POSIX version 6 requires <stdint.h>
-#     if defined(_POSIX_VERSION) && (_POSIX_VERSION >= 200100) && (_POSIX_C_SOURCE >= 200100)
+#     if defined(_POSIX_VERSION) && (_POSIX_VERSION >= 200100)
 #        define BOOST_HAS_STDINT_H
 #     endif
 
       // POSIX version 2 requires <dirent.h>
-#     if defined(_POSIX_VERSION) && (_POSIX_VERSION >= 199009L) && (_POSIX_C_SOURCE >= 199009L)
+#     if defined(_POSIX_VERSION) && (_POSIX_VERSION >= 199009L)
 #        define BOOST_HAS_DIRENT_H
 #     endif
 
@@ -69,10 +69,13 @@
       // BOOST_HAS_PTHREAD_MUTEXATTR_SETTYPE:
       // These are predicated on _XOPEN_VERSION, and appears to be first released
       // in issue 4, version 2 (_XOPEN_VERSION > 500).
-#     if defined(_XOPEN_VERSION) && (_XOPEN_VERSION+0 >= 500)  && defined(_XOPEN_SOURCE) && (_XOPEN_SOURCE >= 500)
+#     if defined(_XOPEN_VERSION) && (_XOPEN_VERSION+0 >= 500)
 #        define BOOST_HAS_GETTIMEOFDAY
-#        define BOOST_HAS_PTHREAD_MUTEXATTR_SETTYPE
+#        if defined(_XOPEN_SOURCE) && (_XOPEN_SOURCE >= 500)
+#           define BOOST_HAS_PTHREAD_MUTEXATTR_SETTYPE
+#        endif
 #     endif
 
 #  endif
 
+