diff -r 64f32a31cd49 Modules/_struct.c
--- a/Modules/_struct.c	Fri Dec 13 12:09:05 2013 +0200
+++ b/Modules/_struct.c	Sat Dec 14 12:12:26 2013 +0800
@@ -1389,7 +1389,7 @@
     }
     else {
         PyErr_Format(PyExc_TypeError,
-                     "Struct() argument 1 must be string, not %s",
+                     "Struct() argument 1 must be string or unicode, not %s",
                      Py_TYPE(o_format)->tp_name);
         return -1;
     }