--- svn-freebsd/sys/netinet/in_mcast.c	2009-09-07 18:57:29.000000000 +0300
+++ temp/sys/netinet/in_mcast.c	2009-09-08 14:41:18.000000000 +0300
@@ -1966,6 +1966,10 @@
 	idx = imo_match_group(imo, ifp, &gsa->sa);
 	if (idx == -1) {
 		is_new = 1;
+	} else if (sopt->sopt_name == IP_ADD_MEMBERSHIP) {
+		/* Trying to join the same Any-source group again. */
+		error = EADDRINUSE;
+		goto out_inp_locked;
 	} else {
 		inm = imo->imo_membership[idx];
 		imf = &imo->imo_mfilters[idx];