diff --git a/django/views/static.py b/django/views/static.py
index 8355950fe0..32feee8b6e 100644
--- a/django/views/static.py
+++ b/django/views/static.py
@@ -56,10 +56,10 @@ def serve(request, path, document_root=None, show_indexes=False):
         raise Http404, '"%s" does not exist' % fullpath
     # Respect the If-Modified-Since header.
     statobj = os.stat(fullpath)
+    mimetype = mimetypes.guess_type(fullpath)[0] or 'application/octet-stream'
     if not was_modified_since(request.META.get('HTTP_IF_MODIFIED_SINCE'),
                               statobj[stat.ST_MTIME], statobj[stat.ST_SIZE]):
-        return HttpResponseNotModified()
-    mimetype = mimetypes.guess_type(fullpath)[0] or 'application/octet-stream'
+        return HttpResponseNotModified(mimetype=mimetype)
     contents = open(fullpath, 'rb').read()
     response = HttpResponse(contents, mimetype=mimetype)
     response["Last-Modified"] = http_date(statobj[stat.ST_MTIME])