diff --git a/app/controllers/wiki_controller.rb b/app/controllers/wiki_controller.rb
index 8a021e44..49c4c04b 100644
--- a/app/controllers/wiki_controller.rb
+++ b/app/controllers/wiki_controller.rb
@@ -459,7 +459,7 @@ EOL
         end
         dir = Rails.root.join('public')
         Dir["#{dir}/**/*"].each do |f|
-          zip_out.add "public#{f.sub(dir,'')}", f
+          zip_out.add "public#{f.sub(dir.to_s,'')}", f
         end
       end
       files = @web.files_path