diff -r 09736ae1c314 Lib/tokenize.py
--- a/Lib/tokenize.py	Mon Jun 04 22:52:12 2012 +0200
+++ b/Lib/tokenize.py	Tue Jun 05 00:57:34 2012 +0200
@@ -401,7 +401,7 @@ def detect_encoding(readline):
                 else:
                     msg = 'encoding problem for {!r}: utf-8'.format(filename)
                 raise SyntaxError(msg)
-            encoding += '-sig'
+            encoding = codec.name + '-sig'
         return encoding
 
     first = read_or_stop()