diff --git a/sys/sys/sysctl.h b/sys/sys/sysctl.h
index b570b8c3b45..ed20e503098 100644
--- a/sys/sys/sysctl.h
+++ b/sys/sys/sysctl.h
@@ -87,6 +87,8 @@ struct ctlname {
 #define CTLFLAG_DYN	0x02000000	/* Dynamic oid - can be freed */
 #define CTLFLAG_SKIP	0x01000000	/* Skip this sysctl when listing */
 #define CTLMASK_SECURE	0x00F00000	/* Secure level */
+#define CTLFLAG_TUN	0x00080000	/* Tunable variable */
+#define CTLFLAG_RDTUN	(CTLFLAG_RD|CTLFLAG_TUN)
 
 /*
  * Secure level.   Note that CTLFLAG_SECURE == CTLFLAG_SECURE1.