diff --git a/media-source/mediasource-endofstream.html b/media-source/mediasource-endofstream.html
index bca80af81623bd..5b6114fa716aa3 100644
--- a/media-source/mediasource-endofstream.html
+++ b/media-source/mediasource-endofstream.html
@@ -52,7 +52,8 @@
             // Note that segmentInfo.duration is expected to also be the
             // highest track buffer range end time. Therefore, endOfStream() should
             // not change duration with this media.
-            assert_equals(threeDecimalPlaces(segmentInfo.duration), threeDecimalPlaces(mediaSource.duration));
+            assert_equals(threeDecimalPlaces(segmentInfo.duration), threeDecimalPlaces(mediaSource.duration),
+                'SegmentInfo duration should initially roughly match mediaSource duration');
             assert_less_than_equal(highestEndTime, mediaSource.duration,
                 'Media duration may be slightly longer than intersected track buffered ranges');
 
@@ -64,7 +65,8 @@
             assert_equals(sourceBuffer.buffered.length, 1,
               'Media data properly buffered after endOfStream');
 
-            assert_equals(threeDecimalPlaces(segmentInfo.duration), threeDecimalPlaces(mediaSource.duration));
+            assert_equals(threeDecimalPlaces(segmentInfo.duration), threeDecimalPlaces(mediaSource.duration),
+                'SegmentInfo duration should still roughly match mediaSource duration');
             assert_less_than_equal(highestEndTime, mediaSource.duration,
                 'Media duration may be slightly longer than intersected track buffered ranges');
             assert_equals(sourceBuffer.buffered.end(0), mediaSource.duration,