diff -r 76bc92fb90c1 Lib/wsgiref/simple_server.py
--- a/Lib/wsgiref/simple_server.py	Thu Dec 13 15:44:18 2012 -0800
+++ b/Lib/wsgiref/simple_server.py	Fri Dec 14 09:53:44 2012 +0100
@@ -82,7 +82,11 @@
         else:
             path,query = self.path,''
 
-        env['PATH_INFO'] = urllib.parse.unquote_to_bytes(path).decode('iso-8859-1')
+        enc_path = urllib.parse.unquote_to_bytes(path)
+        try:
+            env['PATH_INFO'] = enc_path.decode('utf-8')
+        except UnicodeDecodeError:
+            env['PATH_INFO'] = enc_path.decode('iso-8859-1')
         env['QUERY_STRING'] = query
 
         host = self.address_string()