diff --git a/include/boost/config/posix_features.hpp b/include/boost/config/posix_features.hpp
index 8bd39e58..b0580f22 100644
--- a/include/boost/config/posix_features.hpp
+++ b/include/boost/config/posix_features.hpp
@@ -32,20 +32,20 @@
 
       // BOOST_HAS_NANOSLEEP:
       // This is predicated on _POSIX_TIMERS or _XOPEN_REALTIME:
-#     if defined(_POSIX_TIMERS) && (_POSIX_TIMERS+0 >= 0)
-#        define BOOST_HAS_NANOSLEEP
-#     endif
-#     if defined(_XOPEN_REALTIME) && (_XOPEN_REALTIME+0 >= 0) && !defined(BOOST_HAS_NANOSLEEP)
+      // BOOST_HAS_CLOCK_GETTIME:
+      // This is predicated on _POSIX_TIMERS or _XOPEN_REALTIME:
+#     if (defined(_POSIX_TIMERS) && (_POSIX_TIMERS+0 >= 0)) \
+             || (defined(_XOPEN_REALTIME) && (_XOPEN_REALTIME+0 >= 0))
 #        define BOOST_HAS_NANOSLEEP
+#        define BOOST_HAS_CLOCK_GETTIME
 #     endif
 
       // BOOST_HAS_SCHED_YIELD:
       // This is predicated on _POSIX_PRIORITY_SCHEDULING or
-      // on _POSIX_THREAD_PRIORITY_SCHEDULING.
-#     if defined(_POSIX_PRIORITY_SCHEDULING) && (_POSIX_PRIORITY_SCHEDULING+0 > 0)
-#        define BOOST_HAS_SCHED_YIELD
-#     endif
-#     if defined(_POSIX_THREAD_PRIORITY_SCHEDULING) && (_POSIX_THREAD_PRIORITY_SCHEDULING+0 > 0)
+      // on _POSIX_THREAD_PRIORITY_SCHEDULING or on _XOPEN_REALTIME.
+#     if defined(_POSIX_PRIORITY_SCHEDULING) && (_POSIX_PRIORITY_SCHEDULING+0 > 0)\
+            || (defined(_POSIX_THREAD_PRIORITY_SCHEDULING) && (_POSIX_THREAD_PRIORITY_SCHEDULING+0 > 0))\
+            || (defined(_XOPEN_REALTIME) && (_XOPEN_REALTIME+0 >= 0))
 #        define BOOST_HAS_SCHED_YIELD
 #     endif
 
@@ -58,11 +58,4 @@
 #        define BOOST_HAS_PTHREAD_MUTEXATTR_SETTYPE
 #     endif
 
-      // BOOST_HAS_CLOCK_GETTIME:
-      // This is predicated on _POSIX_TIMERS.
-#     if defined(_POSIX_TIMERS) && (_POSIX_TIMERS+0 > 0)
-#        define BOOST_HAS_CLOCK_GETTIME
-#     endif
-
-
 #  endif