Index: django/contrib/syndication/views.py
===================================================================
--- django/contrib/syndication/views.py	(revision 8063)
+++ django/contrib/syndication/views.py	(working copy)
@@ -1,5 +1,7 @@
 from django.contrib.syndication import feeds
 from django.http import HttpResponse, Http404
+from django.utils.http import http_date
+import time
 
 def feed(request, url, feed_dict=None):
     if not feed_dict:
@@ -21,5 +23,6 @@
         raise Http404, "Invalid feed parameters. Slug %r is valid, but other parameters, or lack thereof, are not." % slug
 
     response = HttpResponse(mimetype=feedgen.mime_type)
+    response['Last-Modified'] = http_date(time.mktime(feedgen.latest_post_date().timetuple()))
     feedgen.write(response, 'utf-8')
     return response