diff --git a/bottle.py b/bottle.py
index 23fff762..7f8e03b9 100755
--- a/bottle.py
+++ b/bottle.py
@@ -1804,7 +1804,7 @@ def headerlist(self):
     expires = HeaderProperty(
         'Expires',
         reader=lambda x: datetime.utcfromtimestamp(parse_date(x)),
-        writer=lambda x: http_date(x))
+        writer=http_date)
 
     @property
     def charset(self, default='UTF-8'):