diff --git a/app/models/application_record.rb b/app/models/application_record.rb
index 014a73997d9..299aad63404 100644
--- a/app/models/application_record.rb
+++ b/app/models/application_record.rb
@@ -22,4 +22,10 @@ class ApplicationRecord < ActiveRecord::Base
       value
     end
   end
+
+  # Prevent implicit serialization in ActiveModel::Serializer or other code paths.
+  # This is a hardening step to avoid accidental leaking of attributes.
+  def as_json
+    raise NotImplementedError
+  end
 end