diff --git a/youtube_dl/extractor/youtube.py b/youtube_dl/extractor/youtube.py
index 4d3bce879..7df79b943 100644
--- a/youtube_dl/extractor/youtube.py
+++ b/youtube_dl/extractor/youtube.py
@@ -344,7 +344,7 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
         elif len(s) == 85:
             return s[2:8] + s[0] + s[9:21] + s[65] + s[22:65] + s[84] + s[66:82] + s[21]
         elif len(s) == 84:
-            return s[83:36:-1] + s[2] + s[35:26:-1] + s[3] + s[25:3:-1] + s[26]
+            return s[83:27:-1] + s[0] + s[26:5:-1] + s[2:0:-1] + s[27]
         elif len(s) == 83:
             return s[:15] + s[80] + s[16:80] + s[15]
         elif len(s) == 82: