diff -r 4b42d7f288c5 Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Thu Jan 03 09:22:41 2013 +0100
+++ b/Objects/unicodeobject.c	Fri Jan 04 11:38:42 2013 +0200
@@ -10542,7 +10542,7 @@
     Py_UCS4 maxchar, maxchar2;
     Py_ssize_t left_len, right_len, new_len;
 
-    if (p_left == NULL) {
+    if (p_left == NULL || *p_left == NULL) {
         if (!PyErr_Occurred())
             PyErr_BadInternalCall();
         return;