diff -r d9a3d23cf8f0 Objects/unicodeobject.c
--- a/Objects/unicodeobject.c	Tue Oct 14 00:53:13 2014 +0200
+++ b/Objects/unicodeobject.c	Tue Oct 14 15:10:15 2014 +0200
@@ -7463,6 +7463,11 @@
     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);