diff --git a/signxml/util/__init__.py b/signxml/util/__init__.py
index 6c4483a..9f0ad96 100644
--- a/signxml/util/__init__.py
+++ b/signxml/util/__init__.py
@@ -25,7 +25,10 @@
 
 class Namespace(dict):
     def __getattr__(self, a):
-        return dict.__getitem__(self, a)
+        try:
+            return dict.__getitem__(self, a)
+        except KeyError:
+            raise AttributeError(a) from None
 
 
 namespaces = Namespace(