diff --git a/db/migrate/20180906094641_add_uniqueness_of_variant_id_to_spree_stock_items.rb b/db/migrate/20180906094641_add_uniqueness_of_variant_id_to_spree_stock_items.rb
index bc7713f428..93b2853208 100644
--- a/db/migrate/20180906094641_add_uniqueness_of_variant_id_to_spree_stock_items.rb
+++ b/db/migrate/20180906094641_add_uniqueness_of_variant_id_to_spree_stock_items.rb
@@ -1,3 +1,6 @@
+# Since OFN has only a single default StockLocation, variants in OFN can only
+# have a stock item. By adding this unique index we constraint that at DB level
+# ensuring data integrity.
 class AddUniquenessOfVariantIdToSpreeStockItems < ActiveRecord::Migration
   def change
     add_index :spree_stock_items, :variant_id, unique: true