diff --git a/lib/core-net/sorted-usec-list.c b/lib/core-net/sorted-usec-list.c
index e9b9c1f6b..d9af0f118 100644
--- a/lib/core-net/sorted-usec-list.c
+++ b/lib/core-net/sorted-usec-list.c
@@ -146,6 +146,12 @@ __lws_sul_service_ripe(lws_dll2_owner_t *own, int own_len, lws_usec_t usnow)
 
 		/* his moment has come... remove him from his owning list */
 
+		if (!hit->cb) {
+			lwsl_err("%s: sul with NULL callback (did not cancel on destory?)\n", __func__);
+
+			return 0;
+		}
+
 		lws_dll2_remove(&hit->list);
 		hit->us = 0;