diff -up bind-9.9.0b1/lib/isc/unix/socket.c.v6only bind-9.9.0b1/lib/isc/unix/socket.c
--- bind-9.9.0b1/lib/isc/unix/socket.c.v6only	2011-11-10 14:35:26.457842491 +0100
+++ bind-9.9.0b1/lib/isc/unix/socket.c	2011-11-10 14:38:55.928827943 +0100
@@ -5726,7 +5726,24 @@ isc__socket_ipv6only(isc_socket_t *sock0
 
 #ifdef IPV6_V6ONLY
 	if (sock->pf == AF_INET6) {
-		if (setsockopt(sock->fd, IPPROTO_IPV6, IPV6_V6ONLY,
+		int current;
+		socklen_t len = sizeof(int);
+		if (getsockopt(sock->fd, IPPROTO_IPV6, IPV6_V6ONLY,
+			      (void *)&current, &len) < 0 ) {
+			char strbuf[ISC_STRERRORSIZE];
+			isc__strerror(errno, strbuf, sizeof(strbuf));
+			UNEXPECTED_ERROR(__FILE__, __LINE__,
+					 "getsockopt(%d, IPV6_V6ONLY) "
+					 "%s: %s", sock->fd,
+					 isc_msgcat_get(isc_msgcat,
+							ISC_MSGSET_GENERAL,
+							ISC_MSG_FAILED,
+							"failed"),
+					 strbuf);
+		}
+
+		if (current != onoff &&
+		    setsockopt(sock->fd, IPPROTO_IPV6, IPV6_V6ONLY,
 			       (void *)&onoff, sizeof(int)) < 0) {
 			char strbuf[ISC_STRERRORSIZE];
 			isc__strerror(errno, strbuf, sizeof(strbuf));