diff --git a/sys/net/route.c b/sys/net/route.c
index 85a4f4264502..1dd12da6ded1 100644
--- a/sys/net/route.c
+++ b/sys/net/route.c
@@ -1590,6 +1590,8 @@ rtrequest1_fib(int req, struct rt_addrinfo *info, struct rtentry **ret_nrt,
 	switch (req) {
 	case RTM_DELETE:
 		if (netmask) {
+			if (dst->sa_len > sizeof(mdst))
+				return (EINVAL);
 			rt_maskedcopy(dst, (struct sockaddr *)&mdst, netmask);
 			dst = (struct sockaddr *)&mdst;
 		}