diff --git a/lib/mp4/webvtt-parser.js b/lib/mp4/webvtt-parser.js
index 84629bf7..f92c54f9 100644
--- a/lib/mp4/webvtt-parser.js
+++ b/lib/mp4/webvtt-parser.js
@@ -62,9 +62,9 @@ const WebVttParser = function() {
           // WebVTT Sample format:
           // Exactly one VTTEmptyCueBox box
           // OR one or more VTTCueBox boxes.
-          var sampleData = mdatBox.slice(mdatOffset, mdatOffset + sample.size);
+          const sampleData = mdatBox.slice(mdatOffset, mdatOffset + sample.size);
           // single vtte box.
-          var vtteBox = findBox(sampleData, ['vtte'])[0];
+          const vtteBox = findBox(sampleData, ['vtte'])[0];
 
           // empty box
           if (vtteBox) {