diff --git a/Lib/test/test_unittest_mock.py b/Lib/test/test_unittest_mock.py
new file mode 100644
index 0000000..88ffa46
--- /dev/null
+++ b/Lib/test/test_unittest_mock.py
@@ -0,0 +1,23 @@
+import unittest
+from unittest import mock
+
+
+class InstanceMethodDoubleMockTest(unittest.TestCase):
+    def test_double_mock(self):
+        class C:
+            def f(self):
+                pass
+
+        c = C()
+
+        with mock.patch.object(c, 'f', autospec=True) as patch1:
+            with mock.patch.object(c, 'f', autospec=True) as patch2:
+                c.f()
+            self.assertEqual(patch2.call_count, 1)
+            self.assertEqual(patch1.call_count, 0)
+            c.f()
+        self.assertEqual(patch1.call_count, 1)
+
+if __name__ == "__main__":
+    unittest.main()
+
diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index 7400fb7..b16f04c 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -2199,6 +2199,11 @@ def create_autospec(spec, spec_set=False, instance=False, _parent=None,
         except AttributeError:
             continue
 
+        # If our autospeccing already created this attribute through
+        # _setup_func above, skip it!
+        if hasattr(mock, entry):
+            continue
+
         kwargs = {'spec': original}
         if spec_set:
             kwargs = {'spec_set': original}