diff --git a/youtube_dl/extractor/youtube.py b/youtube_dl/extractor/youtube.py
index da202b9bce..8619f38381 100644
--- a/youtube_dl/extractor/youtube.py
+++ b/youtube_dl/extractor/youtube.py
@@ -1987,7 +1987,8 @@ def _extract_filesize(media_url):
 
                     signature = self._decrypt_signature(
                         encrypted_sig, video_id, player_url, age_gate)
-                    url += '&signature=' + signature
+                    sp = try_get(url_data, lambda x: x['sp'][0], compat_str) or 'signature'
+                    url += '&%s=%s' % (sp, signature)
                 if 'ratebypass' not in url:
                     url += '&ratebypass=yes'