Index: Objects/typeobject.c
===================================================================
--- Objects/typeobject.c	(revision 66159)
+++ Objects/typeobject.c	(working copy)
@@ -4630,13 +4630,19 @@
 	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 (len < 0) {
-		if (!PyErr_Occurred())
+		if ((err = PyErr_Occurred())) {
+			if (PyErr_GivenExceptionMatches(err, PyExc_TypeError))
+				PyErr_SetString(PyExc_TypeError,
+					"__len__() should return an integer");
+		}
+		else
 			PyErr_SetString(PyExc_ValueError,
 					"__len__() should return >= 0");
 		return -1;
Index: Lib/test/test_builtin.py
===================================================================
--- Lib/test/test_builtin.py	(revision 66159)
+++ Lib/test/test_builtin.py	(working copy)
@@ -623,6 +623,16 @@
             def __len__(self):
                 raise ValueError
         self.assertRaises(ValueError, len, BadSeq())
+        class ReturnTypeCheck:
+            def __init__(self, value):
+                self.value = value
+            def __len__(self):
+                return self.value
+        self.assertRaises(TypeError, len, ReturnTypeCheck("foo"))
+        self.assertRaises(TypeError, len, ReturnTypeCheck(.1))
+        self.assertRaises(ValueError, len, ReturnTypeCheck(-1))
+        self.assertRaises(ValueError, len, ReturnTypeCheck(-1<<50))
+        self.assertEqual(len(ReturnTypeCheck(1<<50)), sys.maxsize)
 
     def test_map(self):
         self.assertEqual(