diff -r 82ae284cd5f1 Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Mon Sep 03 17:29:22 2012 -0400
+++ b/Objects/unicodeobject.c	Tue Sep 04 16:09:09 2012 +1000
@@ -7322,6 +7322,11 @@
     Py_ssize_t offset;
     int chunk_len, ret, done;
 
+    if (!PyUnicode_Check(unicode)) {
+        PyErr_BadArgument();
+        return NULL;
+    }
+
     if (PyUnicode_READY(unicode) == -1)
         return NULL;
     len = PyUnicode_GET_LENGTH(unicode);