diff --git a/src/controller/timeline-controller.ts b/src/controller/timeline-controller.ts
index 4816b2f8fea..63920fee6d1 100644
--- a/src/controller/timeline-controller.ts
+++ b/src/controller/timeline-controller.ts
@@ -289,7 +289,11 @@ class TimelineController extends EventHandler {
         if (!currentTrack.cues.getCueById(cue.id)) {
           try {
             currentTrack.addCue(cue);
+            if (!currentTrack.cues.getCueById(cue.id)) {
+              throw new Error(`addCue is failed for: ${cue}`);
+            }
           } catch (err) {
+            logger.debug(`Failed occurred on adding cues: ${err}`);
             const textTrackCue = new (window as any).TextTrackCue(cue.startTime, cue.endTime, cue.text);
             textTrackCue.id = cue.id;
             currentTrack.addCue(textTrackCue);