diff --git a/acme/acme/messages.py b/acme/acme/messages.py
index 0e1ffdf7b..d6f836fae 100644
--- a/acme/acme/messages.py
+++ b/acme/acme/messages.py
@@ -199,7 +199,7 @@ class Directory(jose.JSONDeSerializable):
         try:
             return self[name.replace('_', '-')]
         except KeyError as error:
-                raise AttributeError(str(error) + ': ' + name)
+            raise AttributeError(str(error) + ': ' + name)
 
     def __getitem__(self, name):
         try: