diff --git a/youtube_dl/extractor/youtube.py b/youtube_dl/extractor/youtube.py
index 726b5ba0aa..9da8d4bc53 100644
--- a/youtube_dl/extractor/youtube.py
+++ b/youtube_dl/extractor/youtube.py
@@ -1515,7 +1515,7 @@ def _map_to_format_list(urlmap):
             w = float(stretched_m.group('w'))
             h = float(stretched_m.group('h'))
             if w > 0 and h > 0:
-                ratio = float(stretched_m.group('w')) / float(stretched_m.group('h'))
+                ratio = w / h
                 for f in formats:
                     if f.get('vcodec') != 'none':
                         f['stretched_ratio'] = ratio