Index: Objects/typeobject.c
===================================================================
--- Objects/typeobject.c	(revision 66056)
+++ Objects/typeobject.c	(working copy)
@@ -4630,11 +4630,18 @@
 	static PyObject *len_str;
 	PyObject *res = call_method(self, "__len__", &len_str, "()");
 	Py_ssize_t len;
+	PyObject *err;
 
 	if (res == NULL)
 		return -1;
-	len = PyLong_AsSsize_t(res);
+	len = PyNumber_AsSsize_t(res, NULL);
 	Py_DECREF(res);
+	if ((err = PyErr_Occurred()) && 
+	    PyErr_GivenExceptionMatches(err, PyExc_TypeError)) {
+		PyErr_SetString(PyExc_TypeError, 
+				"__len__() should return an int");
+		return -1;
+	}
 	if (len < 0) {
 		if (!PyErr_Occurred())
 			PyErr_SetString(PyExc_ValueError,
Index: Lib/test/test_builtin.py
===================================================================
--- Lib/test/test_builtin.py	(revision 66056)
+++ Lib/test/test_builtin.py	(working copy)
@@ -623,6 +623,10 @@
             def __len__(self):
                 raise ValueError
         self.assertRaises(ValueError, len, BadSeq())
+        class WrongReturnType:
+            def __len__(self):
+                return .5
+        self.assertRaises(TypeError, len, WrongReturnType())
 
     def test_map(self):
         self.assertEqual(