diff --git a/app/controllers/attachments_controller.rb b/app/controllers/attachments_controller.rb
index 4ef929896..edae9b0cc 100644
--- a/app/controllers/attachments_controller.rb
+++ b/app/controllers/attachments_controller.rb
@@ -52,19 +52,22 @@ class AttachmentsController < ApplicationController
       @attachment.increment_download
     end
 
-    # images are sent inline
-    send_file @attachment.diskfile, :filename => filename_for_content_disposition(@attachment.filename),
-                                    :type => detect_content_type(@attachment),
-                                    :disposition => (@attachment.image? ? 'inline' : 'attachment')
-
+    if stale?(:etag => @attachment.digest)
+      # images are sent inline
+      send_file @attachment.diskfile, :filename => filename_for_content_disposition(@attachment.filename),
+                                      :type => detect_content_type(@attachment),
+                                      :disposition => (@attachment.image? ? 'inline' : 'attachment')
+    end
   end
 
   def thumbnail
     if @attachment.thumbnailable? && Setting.thumbnails_enabled? && thumbnail = @attachment.thumbnail
-      send_file thumbnail,
-        :filename => filename_for_content_disposition(@attachment.filename),
-        :type => detect_content_type(@attachment),
-        :disposition => 'inline'
+      if stale?(:etag => thumbnail)
+        send_file thumbnail,
+          :filename => filename_for_content_disposition(@attachment.filename),
+          :type => detect_content_type(@attachment),
+          :disposition => 'inline'
+      end
     else
       # No thumbnail for the attachment or thumbnail could not be created
       render :nothing => true, :status => 404