diff -r 82451c88b3c0 Lib/encodings/idna.py
--- a/Lib/encodings/idna.py	Thu Apr 11 19:18:22 2013 -0500
+++ b/Lib/encodings/idna.py	Sat Apr 13 13:14:34 2013 -0400
@@ -162,9 +162,9 @@
             labels = result.split(b'.')
             for label in labels[:-1]:
                 if not (0 < len(label) < 64):
-                    raise UnicodeError("label empty or too long")
+                    raise UnicodeError("label empty or too long in %s" % result.decode())
             if len(labels[-1]) >= 64:
-                raise UnicodeError("label too long")
+                raise UnicodeError("label too long %s" % labels[-1].decode())
             return result, len(input)
 
         result = bytearray()
diff -r 82451c88b3c0 Lib/test/test_unicode.py
--- a/Lib/test/test_unicode.py	Thu Apr 11 19:18:22 2013 -0500
+++ b/Lib/test/test_unicode.py	Sat Apr 13 13:14:34 2013 -0400
@@ -1673,6 +1673,21 @@
         # Test whether trailing dot is preserved
         self.assertEqual("www.python.org.".encode("idna"), b"www.python.org.")
 
+    def test_codecs_errors_messages(self):
+        # Test Empty
+        self.assertRaisesRegexp(UnicodeError, 'label empty or too long in 1..com', "1..com".encode, 'idna')
+        # Test label greater then 64
+        label = "A" * 64
+        value = "first." + label + ".last"
+        self.assertRaisesRegexp(UnicodeError, 'label empty or too long in first.%s.last' % label, value.encode, 'idna')
+        # Test last label length 64
+        value = "first.second." + label
+        self.assertRaisesRegexp(UnicodeError, "label too long " + label, value.encode, 'idna')
+        # Test last label length greater then 64
+        label += "A"
+        value += "A"
+        self.assertRaisesRegexp(UnicodeError, "label too long " + label, value.encode, 'idna')
+
     def test_codecs_errors(self):
         # Error handling (encoding)
         self.assertRaises(UnicodeError, 'Andr\202 x'.encode, 'ascii')