usage
diff --git a/Doc/library/collections.rst b/Doc/library/collections.rst
index 3b49a74..a66b555 100644
--- a/Doc/library/collections.rst
+++ b/Doc/library/collections.rst
@@ -380,7 +380,7 @@
.. method:: defaultdict.__missing__(key)
- If the :attr:`default_factory` attribute is ``None``, this raises an
+ If the :attr:`default_factory` attribute is ``None``, this raises a
:exc:`KeyError` exception with the *key* as argument.
If :attr:`default_factory` is not ``None``, it is called without arguments