diff --git a/sys/kern/kern_mbuf.c b/sys/kern/kern_mbuf.c
--- a/sys/kern/kern_mbuf.c
+++ b/sys/kern/kern_mbuf.c
@@ -1212,6 +1212,7 @@
 			break;
 		case EXT_SFBUF:
 		case EXT_NET_DRV:
+		case EXT_CTL:
 		case EXT_MOD_TYPE:
 		case EXT_DISPOSABLE:
 			KASSERT(mref->m_ext.ext_free != NULL,
diff --git a/sys/sys/mbuf.h b/sys/sys/mbuf.h
--- a/sys/sys/mbuf.h
+++ b/sys/sys/mbuf.h
@@ -593,6 +593,7 @@
 #define	EXT_PACKET	6	/* mbuf+cluster from packet zone */
 #define	EXT_MBUF	7	/* external mbuf reference */
 #define	EXT_RXRING	8	/* data in NIC receive ring */
+#define	EXT_CTL		9	/* buffer from a ctl(4) backend */
 
 #define	EXT_VENDOR1	224	/* for vendor-internal use */
 #define	EXT_VENDOR2	225	/* for vendor-internal use */