diff -r 5376b3a168c8 Doc/library/unittest.mock.rst
--- a/Doc/library/unittest.mock.rst	Thu Dec 08 09:01:39 2016 -0800
+++ b/Doc/library/unittest.mock.rst	Thu Dec 08 22:25:18 2016 +0100
@@ -303,26 +303,26 @@
 
     .. method:: assert_called_once_with(*args, **kwargs)
 
-       Assert that the mock was called exactly once and with the specified
-       arguments.
+       Assert that the mock was called exactly once and that that call was
+       with the specified arguments.
 
             >>> mock = Mock(return_value=None)
             >>> mock('foo', bar='baz')
             >>> mock.assert_called_once_with('foo', bar='baz')
-            >>> mock('foo', bar='baz')
-            >>> mock.assert_called_once_with('foo', bar='baz')
+            >>> mock('other', bar='values')
+            >>> mock.assert_called_once_with('other', bar='values')
             Traceback (most recent call last):
               ...
             AssertionError: Expected 'mock' to be called once. Called 2 times.
 
-
     .. method:: assert_any_call(*args, **kwargs)
 
         assert the mock has been called with the specified arguments.
 
         The assert passes if the mock has *ever* been called, unlike
         :meth:`assert_called_with` and :meth:`assert_called_once_with` that
-        only pass if the call is the most recent one.
+        only pass if the call is the most recent one, and in the case of
+        :meth:`assert_called_once_with` it must also be the only call.
 
             >>> mock = Mock(return_value=None)
             >>> mock(1, 2, arg='thing')
diff -r 5376b3a168c8 Lib/unittest/mock.py
--- a/Lib/unittest/mock.py	Thu Dec 08 09:01:39 2016 -0800
+++ b/Lib/unittest/mock.py	Thu Dec 08 22:25:18 2016 +0100
@@ -815,8 +815,8 @@
 
 
     def assert_called_once_with(_mock_self, *args, **kwargs):
-        """assert that the mock was called exactly once and with the specified
-        arguments."""
+        """assert that the mock was called exactly once and that that call was
+        with the specified arguments."""
         self = _mock_self
         if not self.call_count == 1:
             msg = ("Expected '%s' to be called once. Called %s times." %