diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -922,6 +922,9 @@
             seen.add(_new_parent_id)
 
         ret_val = DEFAULT
+        if self.call_count == 1:
+            if not _callable(self.side_effect and self.side_effect is not None):
+                self.side_effect = _try_iter(self.side_effect)
         effect = self.side_effect
         if effect is not None:
             if _is_exception(effect):
diff --git a/Lib/unittest/test/testmock/testmock.py b/Lib/unittest/test/testmock/testmock.py
--- a/Lib/unittest/test/testmock/testmock.py
+++ b/Lib/unittest/test/testmock/testmock.py
@@ -154,6 +154,13 @@
         mock = Mock(side_effect=side_effect, return_value=sentinel.RETURN)
         self.assertEqual(mock(), sentinel.RETURN)
 
+        # Test for issue17826
+        def f(): pass
+        mock = create_autospec(f)
+        mock.side_effect = [1, 2, 3]
+        self.assertEqual([mock(), mock(), mock()], [1, 2, 3],
+                          "side effect not used correctly in create_autospec")
+
 
     @unittest.skipUnless('java' in sys.platform,
                           'This test only applies to Jython')