diff -r 953d8ec1aeb3 Lib/test/test_struct.py
--- a/Lib/test/test_struct.py	Sat Dec 14 21:07:51 2013 +0200
+++ b/Lib/test/test_struct.py	Sun Dec 15 22:37:33 2013 +0800
@@ -659,6 +659,13 @@
         self.assertRaises(StopIteration, next, it)
         self.assertRaises(StopIteration, next, it)
 
+    def test_invalid_argument(self):
+        with self.assertRaises(TypeError) as cx:
+            struct.Struct(1)
+        self.assertEqual(str(cx.exception),
+                         "Struct() argument 1 must be a string or bytes "
+                         "object, not int")
+
 
 def test_main():
     support.run_unittest(__name__)
diff -r 953d8ec1aeb3 Modules/_struct.c
--- a/Modules/_struct.c	Sat Dec 14 21:07:51 2013 +0200
+++ b/Modules/_struct.c	Sun Dec 15 22:37:33 2013 +0800
@@ -1432,8 +1432,8 @@
     if (!PyBytes_Check(o_format)) {
         Py_DECREF(o_format);
         PyErr_Format(PyExc_TypeError,
-                     "Struct() argument 1 must be a bytes object, not %.200s",
-                     Py_TYPE(o_format)->tp_name);
+                     "Struct() argument 1 must be a string or bytes object, "
+                     "not %.200s", Py_TYPE(o_format)->tp_name);
         return -1;
     }