diff --git a/src/sipevent/listen.c b/src/sipevent/listen.c
index 1c498a5..0efae54 100644
--- a/src/sipevent/listen.c
+++ b/src/sipevent/listen.c
@@ -187,7 +187,11 @@ static void notify_handler(struct sipevent_sock *sock,
 
 	if (sub->refer_cseq >= 0 && !sub->id && pl_isset(&event.id)) {
 
-		(void)pl_strdup(&sub->id, &event.id);
+		err = pl_strdup(&sub->id, &event.id);
+		if (err) {
+			(void)sip_treply(NULL, sip, msg, 500, strerror(err));
+			return;
+		}
 	}
 
 	re_printf("notify: %s (%r)\n", sipevent_substate_name(state.state),