--- ntp-4.2.4/ntpd/ntp_peer.c.loopback	2006-12-28 13:03:31.000000000 +0100
+++ ntp-4.2.4/ntpd/ntp_peer.c	2007-01-07 09:24:54.000000000 +0100
@@ -664,9 +664,13 @@
 	 * This might happen in some systems and would preclude proper
 	 * operation with public key cryptography.
 	 */
-	if (ISREFCLOCKADR(srcadr))
+	if (ISREFCLOCKADR(srcadr)) {
+		if (!loopback_interface) {
+			netsyslog(LOG_ERR, "missing loopback interface!");
+			exit(1);
+		}
 		interface = loopback_interface;
-	else
+	} else
 		if (cast_flags & (MDF_BCLNT | MDF_ACAST | MDF_MCAST | MDF_BCAST)) {
 			interface = findbcastinter(srcadr);
 #ifdef DEBUG