diff --git a/docs/compatible_idioms.rst b/docs/compatible_idioms.rst
index 7eb0cfb6..e48ac6d1 100644
--- a/docs/compatible_idioms.rst
+++ b/docs/compatible_idioms.rst
@@ -1120,7 +1120,7 @@ cmp()
 .. code:: python
 
     # Python 2 and 3: alternative 2
-    cmp = lambda x, y: (x > y) - (x < y)
+    cmp = lambda(x, y): (x > y) - (x < y)
     assert cmp('a', 'b') < 0 and cmp('b', 'a') > 0 and cmp('c', 'c') == 0
 reload()
 ~~~~~~~~