diff --git a/htdocs/install/mysql/tables/llx_adherent.key.sql b/htdocs/install/mysql/tables/llx_adherent.key.sql
index 2b176bef2d1..750caff808a 100644
--- a/htdocs/install/mysql/tables/llx_adherent.key.sql
+++ b/htdocs/install/mysql/tables/llx_adherent.key.sql
@@ -19,6 +19,7 @@
 
 
 ALTER TABLE llx_adherent ADD UNIQUE INDEX uk_adherent_login (login, entity);
+ALTER TABLE llx_adherent ADD UNIQUE INDEX uk_adherent_ref (ref, entity);
 ALTER TABLE llx_adherent ADD UNIQUE INDEX uk_adherent_fk_soc (fk_soc);
 
 ALTER TABLE llx_adherent ADD INDEX idx_adherent_fk_adherent_type (fk_adherent_type);