diff --git a/content/media/gstreamer/GStreamerReader.cpp b/content/media/gstreamer/GStreamerReader.cpp
index b64ef9daefc4..df908bc853d8 100644
--- a/content/media/gstreamer/GStreamerReader.cpp
+++ b/content/media/gstreamer/GStreamerReader.cpp
@@ -711,12 +711,15 @@ int64_t GStreamerReader::QueryDuration()
     }
   }
 
-  /*if (mDecoder->mDuration != -1 &&
-      mDecoder->mDuration > duration) {
-    // We decoded more than the reported duration (which could be estimated)
-    LOG(PR_LOG_DEBUG, ("mDuration > duration"));
-    duration = mDecoder->mDuration;
-  }*/
+  {
+    ReentrantMonitorAutoEnter mon(mDecoder->GetReentrantMonitor());
+    int64_t media_duration = mDecoder->GetMediaDuration();
+    if (media_duration != -1 && media_duration > duration) {
+      // We decoded more than the reported duration (which could be estimated)
+      LOG(PR_LOG_DEBUG, ("decoded duration > estimated duration"));
+      duration = media_duration;
+    }
+  }
 
   return duration;
 }