diff --git a/htdocs/install/mysql/tables/llx_actioncomm.sql b/htdocs/install/mysql/tables/llx_actioncomm.sql
index 0dbb4e1d1a7..9012f6b3a66 100644
--- a/htdocs/install/mysql/tables/llx_actioncomm.sql
+++ b/htdocs/install/mysql/tables/llx_actioncomm.sql
@@ -24,7 +24,7 @@
 create table llx_actioncomm
 (
   id				integer AUTO_INCREMENT PRIMARY KEY,
-  ref               varchar(30),
+  ref               varchar(30) NOT NULL,
   ref_ext			varchar(255),					-- reference into an external system (not used by dolibarr). Example: An id coming from google calendar has length between 5 and 1024 chars. An event id must follow rule: chars used in base32hex encoding (i.e. lowercase letters a-v and digits 0-9, see section 3.1.2 in RFC2938)
   entity			integer DEFAULT 1 NOT NULL,		-- multi company id
   datep				datetime,						-- date start