diff --git a/htdocs/install/mysql/tables/llx_product_attribute.sql b/htdocs/install/mysql/tables/llx_product_attribute.sql
index c81d122d9bb..362c104b95c 100644
--- a/htdocs/install/mysql/tables/llx_product_attribute.sql
+++ b/htdocs/install/mysql/tables/llx_product_attribute.sql
@@ -23,7 +23,7 @@ CREATE TABLE llx_product_attribute
 (
   rowid INT PRIMARY KEY NOT NULL AUTO_INCREMENT,
   ref VARCHAR(255) NOT NULL,
-  ref_ext VARCHAR(255) NOT NULL,
+  ref_ext VARCHAR(255) NULL,
   label VARCHAR(255) NOT NULL,
   rang INT DEFAULT 0 NOT NULL,
   entity INT DEFAULT 1 NOT NULL