diff --git a/youtube_dl/extractor/youtube.py b/youtube_dl/extractor/youtube.py
index 53f13b516..f3b9e3ab1 100644
--- a/youtube_dl/extractor/youtube.py
+++ b/youtube_dl/extractor/youtube.py
@@ -1390,6 +1390,8 @@ class YoutubeIE(YoutubeBaseInfoExtractor, SubtitlesInfoExtractor):
             args = info['args']
             # Easy way to know if the 's' value is in url_encoded_fmt_stream_map
             # this signatures are encrypted
+            if 'url_encoded_fmt_stream_map':
+                raise ValueError(u'No stream_map present')  # caught below
             m_s = re.search(r'[&,]s=', args['url_encoded_fmt_stream_map'])
             if m_s is not None:
                 self.to_screen(u'%s: Encrypted signatures detected.' % video_id)