diff --git a/youtube_dl/extractor/youtube.py b/youtube_dl/extractor/youtube.py
index e573b021d..1599dd484 100644
--- a/youtube_dl/extractor/youtube.py
+++ b/youtube_dl/extractor/youtube.py
@@ -778,13 +778,16 @@ class YoutubeIE(YoutubeBaseInfoExtractor):
                 self.to_screen(u'%s: Encrypted signatures detected.' % video_id)
                 video_info['url_encoded_fmt_stream_map'] = [args['url_encoded_fmt_stream_map']]
             m_s = re.search(r'[&,]s=', args.get('adaptive_fmts', u''))
-            if 'url_encoded_fmt_stream_map' not in video_info or not video_info['url_encoded_fmt_stream_map']:
-                video_info['url_encoded_fmt_stream_map'] = ['']
             if m_s is not None:
-                video_info['url_encoded_fmt_stream_map'][0] += ','+args['adaptive_fmts']
+                if 'url_encoded_fmt_stream_map' in video_info:
+                    video_info['url_encoded_fmt_stream_map'][0] += ',' + args['adaptive_fmts']
+                else:
+                    video_info['url_encoded_fmt_stream_map'] = [args['adaptive_fmts']]
             elif 'adaptive_fmts' in video_info:
-                video_info['url_encoded_fmt_stream_map'][0] += ','+video_info['adaptive_fmts'][0]
-
+                if 'url_encoded_fmt_stream_map' in video_info:
+                    video_info['url_encoded_fmt_stream_map'][0] += ',' + video_info['adaptive_fmts'][0]
+                else:
+                    video_info['url_encoded_fmt_stream_map'] = video_info['adaptive_fmts']
         except ValueError:
             pass