diff --git a/app/controllers/ticket_articles_controller.rb b/app/controllers/ticket_articles_controller.rb
index 786748a5c..35f845a0e 100644
--- a/app/controllers/ticket_articles_controller.rb
+++ b/app/controllers/ticket_articles_controller.rb
@@ -253,7 +253,7 @@ class TicketArticlesController < ApplicationController
     send_data(
       file.content,
       filename: file.filename,
-      type: file.preferences['Content-Type'] || file.preferences['Mime-Type'],
+      type: file.preferences['Content-Type'] || file.preferences['Mime-Type'] || 'application/octet-stream',
       disposition: disposition
     )
   end