diff --git a/usr.sbin/ntp/config.h b/usr.sbin/ntp/config.h
index 51d0929fa6cd..207992c2985b 100644
--- a/usr.sbin/ntp/config.h
+++ b/usr.sbin/ntp/config.h
@@ -453,7 +453,9 @@
 #define HAVE_MKTIME 1
 
 /* Define to 1 if you have the `mlockall' function. */
+#if __FreeBSD_version >= 500102
 #define HAVE_MLOCKALL 1
+#endif
 
 /* Define to 1 if you have the `mrand48' function. */
 #define HAVE_MRAND48 1