diff --git a/app/models/library.rb b/app/models/library.rb
index 90b9737e..6029f984 100644
--- a/app/models/library.rb
+++ b/app/models/library.rb
@@ -2,7 +2,7 @@ class Library < ActiveRecord::Base
   include AASM
 
   belongs_to :user
-  belongs_to :cover, class_name: 'Attachment', foreign_key: :cover_id, optional: true
+  belongs_to :cover, class_name: 'Attachment', foreign_key: :cover_id
 
   has_many :library_applies, dependent: :delete_all
   has_many :attachments, as: :container