diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -302,6 +302,13 @@
 #  else
 #    define _LIBCPP_BIG_ENDIAN
 #  endif
+#  ifndef SEM_VALUE_MAX
+     // <limits.h> doesn't define SEM_VALUE_MAX as allowed by XPG7.  However,
+     // sysconf(_SC_SEM_VALUE_MAX) has returned _SEM_VALUE_MAX since Solaris 2.6.
+#    define _KMEMUSER
+#    include <sys/param.h>
+#    define SEM_VALUE_MAX _SEM_VALUE_MAX
+#  endif
 #endif // __sun__
 
 #if defined(__CloudABI__)