diff --git a/install/sql/incremental/upd_dev_collection.sql b/install/sql/incremental/upd_dev_collection.sql
index 72f0f0376186324ff56893fe00a367c2a6ac09ad..2206658555b653d3bd4600e082faddbbb5b18816 100644
--- a/install/sql/incremental/upd_dev_collection.sql
+++ b/install/sql/incremental/upd_dev_collection.sql
@@ -7,7 +7,7 @@ ALTER TABLE `spamfilter_users` ALTER `policy_id` SET DEFAULT 0;
 
 -- mail_forwarding.source must be unique
 ALTER TABLE `mail_forwarding` DROP KEY `server_id`;
-ALTER TABLE `mail_forwarding` ADD UNIQUE KEY `server_id` (`server_id`, `source`);
+ALTER TABLE `mail_forwarding` ADD KEY `server_id` (`server_id`, `source`);
 
 -- Purge apps & addons installer (#5795) - second time due to syntax error in 0093
 DROP TABLE IF EXISTS `software_package`;