diff --git a/app/models/discuss.rb b/app/models/discuss.rb
index a50b18a6f..e8fee2ed1 100644
--- a/app/models/discuss.rb
+++ b/app/models/discuss.rb
@@ -10,7 +10,7 @@ class Discuss < ApplicationRecord
   has_one :praise_tread_cache, as: :object, dependent: :destroy
   belongs_to :dis, polymorphic: true
 
-  belongs_to :challenge
+  belongs_to :challenge, optional: true
   after_create :send_tiding
 
   scope :children, -> (discuss_id){ where(parent_id: discuss_id).includes(:user).reorder(created_at: :asc) }