diff --git a/youtube_dl/extractor/common.py b/youtube_dl/extractor/common.py
index da192728f..572f91221 100644
--- a/youtube_dl/extractor/common.py
+++ b/youtube_dl/extractor/common.py
@@ -327,7 +327,7 @@ class InfoExtractor(object):
         # we have cached the regexp for *this* class, whereas getattr would also
         # match the superclass
         if '_VALID_URL_RE' not in cls.__dict__:
-            cls._VALID_URL_RE = re.compile(cls._VALID_URL)
+            cls._VALID_URL_RE = re.compile(cls._VALID_URL, flags=re.IGNORECASE)
         return cls._VALID_URL_RE.match(url) is not None
 
     @classmethod