diff --git a/sys/netinet/ip_input.c b/sys/netinet/ip_input.c
index 0d1848204289..a84ed078ac46 100644
--- a/sys/netinet/ip_input.c
+++ b/sys/netinet/ip_input.c
@@ -1957,6 +1957,8 @@ ip_forward(struct mbuf *m, int srcrt, struct sockaddr_in *next_hop)
 					ro = &sp->req->sav->sah->sa_route;
 					if (ro->ro_rt && ro->ro_rt->rt_ifp) {
 						dummyifp.if_mtu =
+						    ro->ro_rt->rt_rmx.rmx_mtu ?
+						    ro->ro_rt->rt_rmx.rmx_mtu :
 						    ro->ro_rt->rt_ifp->if_mtu;
 						dummyifp.if_mtu -= ipsechdr;
 						destifp = &dummyifp;