diff --git a/app/controllers/comments_controller.rb b/app/controllers/comments_controller.rb
index 850886e68..8374e4a91 100644
--- a/app/controllers/comments_controller.rb
+++ b/app/controllers/comments_controller.rb
@@ -22,7 +22,7 @@ class CommentsController < ApplicationController
       @discuss = @hack.discusses.new(reply_params)
       @discuss.hidden = false
       @discuss.user_id = current_user.id
-      @discuss.root_id = params[:parent_id]
+      @discuss.root_id = params[:comments][:parent_id]
       @discuss.save!
     rescue Exception => e
       uid_logger_error("reply discuss failed : #{e.message}")