diff -r 2c27093fd11f Lib/test/test_descr.py
--- a/Lib/test/test_descr.py	Mon Apr 30 06:20:37 2012 +0200
+++ b/Lib/test/test_descr.py	Tue May 01 10:45:31 2012 +0100
@@ -1466,6 +1466,22 @@
         self.assertEqual(x, spam.spamlist)
         self.assertEqual(a, a1)
         self.assertEqual(d, d1)
+        spam_cm = spam.spamlist.__dict__['classmeth']
+        x2, a2, d2 = spam_cm(spam.spamlist, *a, **d)
+        self.assertEqual(x2, spam.spamlist)
+        self.assertEqual(a2, a1)
+        self.assertEqual(d2, d1)
+        class SubSpam(spam.spamlist): pass
+        x2, a2, d2 = spam_cm(SubSpam, *a, **d)
+        self.assertEqual(x2, SubSpam)
+        self.assertEqual(a2, a1)
+        self.assertEqual(d2, d1)
+        with self.assertRaises(TypeError):
+            spam_cm()
+        with self.assertRaises(TypeError):
+            spam_cm(spam.spamlist())
+        with self.assertRaises(TypeError):
+            spam_cm(list)
 
     def test_staticmethods(self):
         # Testing static methods...
diff -r 2c27093fd11f Objects/descrobject.c
--- a/Objects/descrobject.c	Mon Apr 30 06:20:37 2012 +0200
+++ b/Objects/descrobject.c	Tue May 01 10:45:31 2012 +0100
@@ -257,14 +257,52 @@
 classmethoddescr_call(PyMethodDescrObject *descr, PyObject *args,
                       PyObject *kwds)
 {
-    PyObject *func, *result;
+    Py_ssize_t argc;
+    PyObject *self, *func, *result;
 
-    func = PyCFunction_New(descr->d_method, (PyObject *)PyDescr_TYPE(descr));
+    /* Make sure that the first argument is acceptable as 'self' */
+    assert(PyTuple_Check(args));
+    argc = PyTuple_GET_SIZE(args);
+    if (argc < 1) {
+        PyErr_Format(PyExc_TypeError,
+                     "descriptor '%V' of '%.100s' "
+                     "object needs an argument",
+                     descr_name((PyDescrObject *)descr), "?",
+                     PyDescr_TYPE(descr)->tp_name);
+        return NULL;
+    }
+    self = PyTuple_GET_ITEM(args, 0);
+    if (!PyType_Check(self)) {
+        PyErr_Format(PyExc_TypeError,
+                     "descriptor '%V' requires a type "
+                     "but received a '%.100s'",
+                     descr_name((PyDescrObject *)descr), "?",
+                     PyDescr_TYPE(descr)->tp_name,
+                     self->ob_type->tp_name);
+        return NULL;
+    }
+    if (!PyType_IsSubtype((PyTypeObject *)self, PyDescr_TYPE(descr))) {
+        PyErr_Format(PyExc_TypeError,
+                     "descriptor '%V' "
+                     "requires a subtype of '%.100s' "
+                     "but received '%.100s",
+                     descr_name((PyDescrObject *)descr), "?",
+                     PyDescr_TYPE(descr)->tp_name,
+                     self->ob_type->tp_name);
+        return NULL;
+    }
+
+    func = PyCFunction_New(descr->d_method, self);
     if (func == NULL)
         return NULL;
-
+    args = PyTuple_GetSlice(args, 1, argc);
+    if (args == NULL) {
+        Py_DECREF(func);
+        return NULL;
+    }
     result = PyEval_CallObjectWithKeywords(func, args, kwds);
     Py_DECREF(func);
+    Py_DECREF(args);
     return result;
 }