diff --git a/app/site.rb b/app/site.rb
index bfb3152e..2537155c 100644
--- a/app/site.rb
+++ b/app/site.rb
@@ -1,5 +1,6 @@
 get '/site/:username.rss' do |username|
   site = Site[username: username]
+  halt 404 if site.nil?
   content_type :xml
   site.to_rss.to_xml
 end