--- a/testing/web-platform/tests/media-source/mediasource-util.js
+++ b/testing/web-platform/tests/media-source/mediasource-util.js
@@ -300,17 +300,20 @@
         mediaElement.addEventListener(eventName, onEvent);
 
         var i = startingIndex;
         var onAppendDone = function() {
             if (eventFired)
                 return;
 
             i++;
-            MediaSourceUtil.append(test, sourceBuffer, MediaSourceUtil.extractSegmentData(mediaData, segmentInfo.media[i]), onAppendDone);
+            if (i < segmentInfo.media.length)
+            {
+                MediaSourceUtil.append(test, sourceBuffer, MediaSourceUtil.extractSegmentData(mediaData, segmentInfo.media[i]), onAppendDone);
+            }
         };
         MediaSourceUtil.append(test, sourceBuffer, MediaSourceUtil.extractSegmentData(mediaData, segmentInfo.media[i]), onAppendDone);
 
     };
 
     function addExtraTestMethods(test)
     {
         test.eventExpectations_ = new EventExpectationsManager(test);