diff --git a/Lib/functools.py b/Lib/functools.py
index ad1cccc77f0..539dc90ecd8 100644
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -93,4 +93,6 @@ def cmp_to_key(mycmp):
             return mycmp(self.obj, other.obj) >= 0
         def __ne__(self, other):
             return mycmp(self.obj, other.obj) != 0
+        def __hash__(self):
+            raise TypeError('hash not implemented')
     return K
diff --git a/Lib/test/test_functools.py b/Lib/test/test_functools.py
index 1629f7ce4e8..05e19b1399f 100644
--- a/Lib/test/test_functools.py
+++ b/Lib/test/test_functools.py
@@ -345,6 +345,13 @@ class TestCmpToKey(unittest.TestCase):
         self.assertEqual(sorted(range(5), key=functools.cmp_to_key(mycmp)),
                          [4, 3, 2, 1, 0])
 
+    def test_hash(self):
+        def mycmp(x, y):
+            return y - x
+        key = functools.cmp_to_key(mycmp)
+        k = key(10)
+        self.assertRaises(TypeError, hash(k))
+
 class TestTotalOrdering(unittest.TestCase):
 
     def test_total_ordering_lt(self):