diff --git a/devscripts/youtube_genalgo.py b/devscripts/youtube_genalgo.py
index d4546758d..f91e8855d 100644
--- a/devscripts/youtube_genalgo.py
+++ b/devscripts/youtube_genalgo.py
@@ -12,6 +12,9 @@ tests = [
     # 92 - vflQw-fB4 2013/07/17
     ("qwertyuioplkjhgfdsazxcvbnm1234567890QWERTYUIOPLKJHGFDSAZXCVBNM!@#$%^&*()_-+={[]}|:;?/>.<'`~\"",
      "mrtyuioplkjhgfdsazxcvbnq1234567890QWERTY}IOPLKJHGFDSAZXCVBNM!@#$%^&*()_-+={[]\"|:;"),
+    # 91 - vfl79wBKW 2013/07/20 (sporadic)
+    ("qwertyuioplkjhgfdsazxcvbnm1234567890QWERTYUIOPLKJHGFDSAZXCVBNM!@#$%^&*()_-+={[]}|:;?/>.<'`~",
+     "/?;:|}][{=+-_)(*&^%$#@!MNBVCXZASDFGHJKLPOIUYTREWQ09876543.1mnbvcxzasdfghjklpoiu"),
     # 90
     ("qwertyuioplkjhgfdsazxcvbnm1234567890QWERTYUIOPLKJHGFDSAZXCVBNM!@#$%^&*()_-+={[]}|:;?/>.<'`",
      "mrtyuioplkjhgfdsazxcvbne1234567890QWER[YUIOPLKJHGFDSAZXCVBNM!@#$%^&*()_-+={`]}|"),
diff --git a/youtube_dl/extractor/youtube.py b/youtube_dl/extractor/youtube.py
index e5f536e6f..47d5cb7ff 100644
--- a/youtube_dl/extractor/youtube.py
+++ b/youtube_dl/extractor/youtube.py
@@ -420,6 +420,8 @@ class YoutubeIE(YoutubeBaseInfoExtractor, SubtitlesInfoExtractor):
             return s[86:29:-1] + s[88] + s[28:5:-1]
         elif len(s) == 92:
             return s[25] + s[3:25] + s[0] + s[26:42] + s[79] + s[43:79] + s[91] + s[80:83]
+        elif len(s) == 91:
+            return s[84:27:-1] + s[86] + s[26:5:-1]
         elif len(s) == 90:
             return s[25] + s[3:25] + s[2] + s[26:40] + s[77] + s[41:77] + s[89] + s[78:81]
         elif len(s) == 89: