Index: Objects/listobject.c
===================================================================
--- Objects/listobject.c	(revision 61626)
+++ Objects/listobject.c	(working copy)
@@ -2037,7 +2037,7 @@
 	}
 	if (compare == Py_None)
 		compare = NULL;
-	if (compare == NULL && 
+	if (compare != NULL && 
             Py_Py3kWarningFlag &&
 	    PyErr_Warn(PyExc_DeprecationWarning, 
 		       "In 3.x, the cmp argument is no longer supported.") < 0)
Index: Lib/test/test_py3kwarn.py
===================================================================
--- Lib/test/test_py3kwarn.py	(revision 61626)
+++ Lib/test/test_py3kwarn.py	(working copy)
@@ -90,6 +90,16 @@
         with catch_warning() as w:
             self.assertWarning(meth >= func, w, expected)
 
+    def test_sort_cmp_arg(self):
+        expected = "In 3.x, the cmp argument is no longer supported."
+        lst = range(5)
+        cmp = lambda x,y: -1
+
+        with catch_warning() as w:
+            self.assertWarning(lst.sort(cmp=cmp), w, expected)
+        with catch_warning() as w:
+            self.assertWarning(sorted(lst, cmp=cmp), w, expected)
+
     def assertWarning(self, _, warning, expected_message):
         self.assertEqual(str(warning.message), expected_message)