diff --git a/app/models/doctrine.rb b/app/models/doctrine.rb
index 9aab78c..c49efae 100644
--- a/app/models/doctrine.rb
+++ b/app/models/doctrine.rb
@@ -26,6 +26,8 @@ class Doctrine < ApplicationRecord
   end
 
   def subject_ids=(ids)
+    ids = ids.map(&:to_i)
+    
     ids.each do |subject_id|
       record = DoctrineSubject.find_or_initialize_by(doctrine_id: self.id, subject_id: subject_id)