--- src/s_bsd.c.old	2010-08-15 18:36:31.000000000 +0100
+++ src/s_bsd.c	2010-08-15 18:37:58.000000000 +0100
@@ -1078,6 +1078,11 @@
 			    report_error("setsockopt(IP_OPTIONS) %s:%s", cptr);
 	}
 #endif
+#if defined(IPPROTO_IPV6) && defined(IPV6_V6ONLY) && !defined(_WIN32) && defined(INET6)
+	opt = 0;
+	if (setsockopt(fd, IPPROTO_IPV6, IPV6_V6ONLY, (OPT_TYPE *)&opt, sizeof(opt)) < 0)
+		report_error("setsockopt(IPV6_V6ONLY) %s:%s", cptr);
+#endif
 }