diff --git a/app/models/attachment.rb b/app/models/attachment.rb
index eea80132c..64ac2c2d1 100644
--- a/app/models/attachment.rb
+++ b/app/models/attachment.rb
@@ -156,7 +156,7 @@ class Attachment < ActiveRecord::Base
   end
 
   def title
-    title = filename.to_s
+    title = filename.dup
     if description.present?
       title << " (#{description})"
     end