Index: head/sys/kern/subr_witness.c
===================================================================
--- head/sys/kern/subr_witness.c
+++ head/sys/kern/subr_witness.c
@@ -361,6 +361,8 @@
 static int	witness_voutput(const char *fmt, va_list ap) __printflike(1, 0);
 static void	witness_setflag(struct lock_object *lock, int flag, int set);
 
+FEATURE(witness, "kernel has witness(9) support");
+
 static SYSCTL_NODE(_debug, OID_AUTO, witness, CTLFLAG_RW | CTLFLAG_MPSAFE, NULL,
     "Witness Locking");