diff --git a/signxml/util/__init__.py b/signxml/util/__init__.py
index 7bb7e05..53c66e2 100644
--- a/signxml/util/__init__.py
+++ b/signxml/util/__init__.py
@@ -116,7 +116,8 @@ def iterate_pem(certs):
 
 
 class Namespace(dict):
-    __getattr__ = dict.__getitem__
+    def __getattr__(self, a):
+        return dict.__getitem__(self, a)
 
 
 class XMLProcessor: