diff -r c10ea224392d Lib/test/test_struct.py
--- a/Lib/test/test_struct.py	Sat Dec 14 20:34:33 2013 +0200
+++ b/Lib/test/test_struct.py	Sun Dec 15 17:25:31 2013 +0800
@@ -585,6 +585,13 @@
         self.assertIs(type(s.format), str)
         self.assertRaises(ValueError, struct.Struct, unichr(0x80))
 
+    def test_invalid_argument(self):
+        with self.assertRaises(TypeError) as cx:
+            struct.Struct(1)
+        self.assertEqual(str(cx.exception),
+                         "Struct() argument 1 must be string or unicode, not "
+                         "int")
+
 
 def test_main():
     support.run_unittest(StructTest)
diff -r c10ea224392d Modules/_struct.c
--- a/Modules/_struct.c	Sat Dec 14 20:34:33 2013 +0200
+++ b/Modules/_struct.c	Sun Dec 15 17:25:31 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;
     }