Index: res/res_pjsip_pubsub.c
===================================================================
--- res/res_pjsip_pubsub.c	(revision 410558)
+++ res/res_pjsip_pubsub.c	(working copy)
@@ -762,11 +762,19 @@
 
 	expires_header = pjsip_msg_find_hdr(rdata->msg_info.msg, PJSIP_H_EXPIRES, rdata->msg_info.msg->hdr.next);
 
-	if (expires_header && expires_header->ivalue < endpoint->subscription.minexpiry) {
-		ast_log(LOG_WARNING, "Subscription expiration %d is too brief for endpoint %s. Minimum is %d\n",
-				expires_header->ivalue, ast_sorcery_object_get_id(endpoint), endpoint->subscription.minexpiry);
-		pjsip_endpt_respond_stateless(ast_sip_get_pjsip_endpoint(), rdata, 423, NULL, NULL, NULL);
-		return PJ_TRUE;
+	if (expires_header) {
+		if (expires_header->ivalue == 0) {
+			ast_log(LOG_WARNING, "Susbscription request from endpoint %s rejected. Expiration of 0 is invalid\n",
+					ast_sorcery_object_get_id(endpoint));
+			pjsip_endpt_respond_stateless(ast_sip_get_pjsip_endpoint(), rdata, 400, NULL, NULL, NULL);
+			return PJ_TRUE;
+		}
+		if (expires_header->ivalue < endpoint->subscription.minexpiry) {
+			ast_log(LOG_WARNING, "Subscription expiration %d is too brief for endpoint %s. Minimum is %d\n",
+					expires_header->ivalue, ast_sorcery_object_get_id(endpoint), endpoint->subscription.minexpiry);
+			pjsip_endpt_respond_stateless(ast_sip_get_pjsip_endpoint(), rdata, 423, NULL, NULL, NULL);
+			return PJ_TRUE;
+		}
 	}
 
 	event_header = pjsip_msg_find_hdr_by_name(rdata->msg_info.msg, &str_event_name, rdata->msg_info.msg->hdr.next);