diff --git a/sys/kern/subr_rman.c b/sys/kern/subr_rman.c
--- a/sys/kern/subr_rman.c
+++ b/sys/kern/subr_rman.c
@@ -205,6 +205,8 @@
 rman_reserve_resource(struct rman *rm, u_long start, u_long end, u_long count,
 		      u_int flags, device_t dev)
 {
+	if (count == 0)
+		return (NULL);
 	u_int	want_activate;
 	struct	resource *r, *s, *rv;
 	u_long	rstart, rend;