diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index 2430b145c1..789134ee32 100644
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -1939,7 +1939,8 @@ static enum sip_result __sip_reliable_xmit(struct sip_pvt *p, int seqno, int res
 	pkt->next = p->packets;
 	pkt->owner = p;
 	pkt->seqno = seqno;
-	pkt->flags = resp;
+	if (resp)
+		ast_set_flag(pkt->flags, FLAG_RESPONSE);
 	pkt->data[len] = '\0';
 	pkt->timer_t1 = p->timer_t1;	/* Set SIP timer T1 */
 	if (fatal)