diff --git a/sys/kern/subr_unit.c b/sys/kern/subr_unit.c
index 910020d9c48..764f26f6784 100644
--- a/sys/kern/subr_unit.c
+++ b/sys/kern/subr_unit.c
@@ -714,6 +714,7 @@ free_unr(struct unrhdr *uh, u_int item)
 {
 	void *p1, *p2;
 
+	WITNESS_WARN(WARN_GIANTOK | WARN_SLEEPOK, NULL, "free_unr");
 	p1 = Malloc(sizeof(struct unr));
 	p2 = Malloc(sizeof(struct unr));
 	mtx_lock(uh->mtx);