diff -r 92fc6850dea0 Modules/_tkinter.c
--- a/Modules/_tkinter.c	Tue Feb 04 14:27:14 2014 -0800
+++ b/Modules/_tkinter.c	Wed Feb 05 00:03:28 2014 +0100
@@ -1397,6 +1397,9 @@
     if (PyUnicode_Check(in)) {
         Py_ssize_t size;
         s = PyUnicode_AsUTF8AndSize(in, &size);
+        if (s == NULL) {
+            return 0;
+        }
         if (size > INT_MAX) {
             PyErr_SetString(PyExc_OverflowError, "string is too long");
             return 0;