diff --git a/modules/sale_promotion_coupon/sale.py b/modules/sale_promotion_coupon/sale.py
index cebcceb171..1df774e7fe 100644
--- a/modules/sale_promotion_coupon/sale.py
+++ b/modules/sale_promotion_coupon/sale.py
@@ -155,6 +155,7 @@ class PromotionCouponNumber(DeactivableMixin, ModelSQL, ModelView):
     def check_unique(cls, numbers, field_names=None):
         if field_names and not (field_names & {'number', 'coupon'}):
             return
+        cls.lock()
         duplicates = []
         for sub_numbers in grouped_slice(numbers):
             domain = ['OR']