diff --git a/app/models/todos/undone_todos_query.rb b/app/models/todos/undone_todos_query.rb
index b4980870..18a630ac 100644
--- a/app/models/todos/undone_todos_query.rb
+++ b/app/models/todos/undone_todos_query.rb
@@ -27,6 +27,9 @@ module Todos
 
       if params[:tag]
         tag = Tag.where(:name => params[:tag]).first
+       if not tag
+         return []
+       end
         not_done_todos = not_done_todos.joins(:taggings).where('taggings.tag_id = ?', tag.id)
       end