diff --git a/slirp/udp.c b/slirp/udp.c
index 8cc6cb66da5e5b666402207cb0af06f95efc8971..f77e00f5a072d0ad203eec31fe09cea34d2e4e29 100644
--- a/slirp/udp.c
+++ b/slirp/udp.c
@@ -152,7 +152,7 @@ udp_input(register struct mbuf *m, int iphlen)
 	 * Locate pcb for datagram.
 	 */
 	so = slirp->udp_last_so;
-	if (so->so_lport != uh->uh_sport ||
+	if (so == &slirp->udb || so->so_lport != uh->uh_sport ||
 	    so->so_laddr.s_addr != ip->ip_src.s_addr) {
 		struct socket *tmp;