--- a/pjlib/src/pj/sock_bsd.c
+++ b/pjlib/src/pj/sock_bsd.c
@@ -539,6 +539,10 @@
 	    pj_sock_setsockopt(*sock, pj_SOL_SOCKET(), pj_SO_NOSIGPIPE(),
 			       &val, sizeof(val));
 	}
+	if (af != PJ_AF_INET) { /* Linux Kernel 2.4.21; June 2003 */
+	    pj_sock_setsockopt(*sock, PJ_SOL_IPV6, IPV6_V6ONLY,
+			       &val, sizeof(val));
+	}
 #if defined(PJ_IPHONE_OS_HAS_MULTITASKING_SUPPORT) && \
     PJ_IPHONE_OS_HAS_MULTITASKING_SUPPORT!=0
 	if (type == pj_SOCK_DGRAM()) {