--- Include/object.h	2005/06/27 21:49:31	1.1
+++ Include/object.h	2005/06/27 21:54:21
@@ -495,6 +495,9 @@
 #define Py_TPFLAGS_HAVE_STACKLESS_EXTENSION 0
 #endif
 
+/* Set if the builtin type (HEAPTYPE is false) can be altered */
+#define Py_TPFLAGS_MUTABLE_BUILTIN (1L<<17)
+
 #define Py_TPFLAGS_DEFAULT  ( \
                              Py_TPFLAGS_HAVE_GETCHARBUFFER | \
                              Py_TPFLAGS_HAVE_SEQUENCE_IN | \
--- Objects/typeobject.c	2005/06/27 21:52:06	1.1
+++ Objects/typeobject.c	2005/06/27 21:52:54
@@ -2079,7 +2079,7 @@
 static int
 type_setattro(PyTypeObject *type, PyObject *name, PyObject *value)
 {
-	if (!(type->tp_flags & Py_TPFLAGS_HEAPTYPE)) {
+	if (!(type->tp_flags & (Py_TPFLAGS_HEAPTYPE | Py_TPFLAGS_MUTABLE_BUILTIN))) {
 		PyErr_Format(
 			PyExc_TypeError,
 			"can't set attributes of built-in/extension type '%s'",