diff --git a/youtube_dl/utils.py b/youtube_dl/utils.py
index c9702fd93..dc73f3407 100644
--- a/youtube_dl/utils.py
+++ b/youtube_dl/utils.py
@@ -63,6 +63,8 @@ from .socks import (
 
 def register_socks_protocols():
     # "Register" SOCKS protocols
+    # In Python < 2.6.5, urlsplit() suffers from bug https://bugs.python.org/issue7904
+    # URLs with protocols not in urlparse.uses_netloc are not handled correctly
     for scheme in ('socks', 'socks4', 'socks4a', 'socks5'):
         if scheme not in compat_urlparse.uses_netloc:
             compat_urlparse.uses_netloc.append(scheme)