Index: head/sbin/newfs/newfs.c
===================================================================
--- head/sbin/newfs/newfs.c
+++ head/sbin/newfs/newfs.c
@@ -398,6 +398,10 @@
 		if (pp != NULL)
 			pp->p_size *= secperblk;
 	}
+	if (getosreldate() < __FreeBSD_version) {
+		warnx("%s is newer than the running kernel and may not be compatible",
+		    getprogname());
+	}
 	mkfs(pp, special);
 	ufs_disk_close(&disk);
 	if (!jflag)