diff --git a/Lib/urllib/error.py b/Lib/urllib/error.py
index 300c3fe..d05f850 100644
--- a/Lib/urllib/error.py
+++ b/Lib/urllib/error.py
@@ -13,6 +13,9 @@
 
 import urllib.response
 
+__all__ = ['URLError', 'HTTPError', 'ContentTooShortError']
+
+
 # do these error classes make sense?
 # make sure all of the IOError stuff is overridden.  we just want to be
 # subtypes.