diff --git a/youtube_dl/extractor/vimeo.py b/youtube_dl/extractor/vimeo.py
index 421795b94..6f947515e 100644
--- a/youtube_dl/extractor/vimeo.py
+++ b/youtube_dl/extractor/vimeo.py
@@ -523,7 +523,7 @@ class VimeoIE(VimeoBaseInfoExtractor):
         urls = []
         # Look for embedded (iframe) Vimeo player
         for mobj in re.finditer(
-                r'<iframe[^>]+?src=(["\'])(?P<url>(?:https?:)?//player\.vimeo\.com/video/\d+.*?)\1',
+                r'<iframe[^>]+?src=(["\']?)(?P<url>(?:https?:)?//player\.vimeo\.com/video/\d+.*?)\1',
                 webpage):
             urls.append(VimeoIE._smuggle_referrer(unescapeHTML(mobj.group('url')), url))
         PLAIN_EMBED_RE = (