diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index 95570aa..324cf39 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -731,8 +731,8 @@
         arguments."""
         self = _mock_self
         if not self.call_count == 1:
-            msg = ("Expected to be called once. Called %s times." %
-                   self.call_count)
+            msg = ("Expected '%s' to be called once. Called %s times." %
+                   (self._mock_name or 'mock', self.call_count))
             raise AssertionError(msg)
         return self.assert_called_with(*args, **kwargs)
 
diff --git a/Lib/unittest/test/testmock/testmock.py b/Lib/unittest/test/testmock/testmock.py
index 64fd1a1..2c6f128 100644
--- a/Lib/unittest/test/testmock/testmock.py
+++ b/Lib/unittest/test/testmock/testmock.py
@@ -463,6 +463,13 @@
                                 mock.assert_called_with)
 
 
+    def test_assert_called_once_with_message(self):
+        mock = Mock(name='geoffrey')
+        self.assertRaisesRegex(AssertionError,
+                     r"Expected 'geoffrey' to be called once\.",
+                     mock.assert_called_once_with)
+
+
     def test__name__(self):
         mock = Mock()
         self.assertRaises(AttributeError, lambda: mock.__name__)