diff -r ee1ef5a97e8f Lib/unittest/mock.py
--- a/Lib/unittest/mock.py	Thu Oct 08 11:34:07 2015 -0700
+++ b/Lib/unittest/mock.py	Thu Oct 08 15:07:42 2015 -0700
@@ -820,7 +820,7 @@
             if expected not in all_calls:
                 raise AssertionError(
                     'Calls not found.\nExpected: %r\n'
-                    'Actual: %r' % (calls, self.mock_calls)
+                    'Actual: %r' % (_CallList(calls), self.mock_calls)
                 ) from cause
             return