diff --git a/app/helpers/files_helper.rb b/app/helpers/files_helper.rb
index 2ec7e6f45..de87b5c8a 100644
--- a/app/helpers/files_helper.rb
+++ b/app/helpers/files_helper.rb
@@ -116,6 +116,7 @@ module FilesHelper
 
   def attachment_candown attachment
     candown = false
+    if attachment.container
     if attachment.container.class.to_s != "HomeworkAttach" && (attachment.container.has_attribute?(:project) || attachment.container.has_attribute?(:project_id)) && attachment.container.project
       project = attachment.container.project
       candown= User.current.member_of?(project) || (project.is_public && attachment.is_public == 1)
@@ -144,6 +145,7 @@ module FilesHelper
     else
       candown = (attachment.is_public == 1 || attachment.is_public == true)
     end
+    end
     candown
   end