--- a/Objects/exceptions.c	Sun Feb 26 09:39:55 2012 +0200
+++ b/Objects/exceptions.c	Sun Feb 26 17:49:52 2012 +1000
@@ -266,7 +266,24 @@
     PyObject *res = PyException_GetCause(self);
     if (res)
         return res;  /* new reference already returned above */
-    Py_RETURN_NONE;
+    Py_INCREF(Py_Ellipsis);
+    return Py_Ellipsis;
+}
+
+int
+_PyException_SetCauseChecked(PyObject *self, PyObject *arg) {
+    if (arg == Py_Ellipsis) {
+        arg = NULL;
+    } else if (arg != Py_None && !PyExceptionInstance_Check(arg)) {
+        PyErr_SetString(PyExc_TypeError, "exception cause must be None, "
+                        "Ellipsis or derive from BaseException");
+        return -1;
+    } else {
+        /* PyException_SetCause steals a reference */
+        Py_INCREF(arg);
+    }
+    PyException_SetCause(self, arg);
+    return 0;
 }
 
 static int
@@ -274,18 +291,8 @@
     if (arg == NULL) {
         PyErr_SetString(PyExc_TypeError, "__cause__ may not be deleted");
         return -1;
-    } else if (arg == Py_None) {
-        arg = NULL;
-    } else if (!PyExceptionInstance_Check(arg)) {
-        PyErr_SetString(PyExc_TypeError, "exception cause must be None "
-                        "or derive from BaseException");
-        return -1;
-    } else {
-        /* PyException_SetCause steals this reference */
-        Py_INCREF(arg);
     }
-    PyException_SetCause(self, arg);
-    return 0;
+    return _PyException_SetCauseChecked(self, arg);
 }