diff --git a/Lib/dumbdbm.py b/Lib/dumbdbm.py
index 45a2f36..16a0d83 100644
--- a/Lib/dumbdbm.py
+++ b/Lib/dumbdbm.py
@@ -24,6 +24,8 @@
 _os = __import__('os')
 import __builtin__
 
+__all__ = ["open"]
+
 _open = __builtin__.open
 
 _BLOCKSIZE = 512