diff --git a/main/install/dokeos_main.sql b/main/install/dokeos_main.sql
index da693cd680..59a2ca543c 100644
--- a/main/install/dokeos_main.sql
+++ b/main/install/dokeos_main.sql
@@ -993,7 +993,7 @@ CREATE TABLE user_field_options (
 DROP TABLE IF EXISTS user_field_values;
 CREATE TABLE user_field_values(
 	id	int	NOT NULL auto_increment,
-	user_id	int	NOT NULL,
+	user_id	int	unsigned NOT NULL,
 	field_id int NOT NULL,
 	field_value	text,
 	tms TIMESTAMP,
diff --git a/main/install/migrate-db-1.8.5-1.8.6-pre.sql b/main/install/migrate-db-1.8.5-1.8.6-pre.sql
index 6187b10f91..081c07f529 100644
--- a/main/install/migrate-db-1.8.5-1.8.6-pre.sql
+++ b/main/install/migrate-db-1.8.5-1.8.6-pre.sql
@@ -43,6 +43,7 @@ INSERT INTO settings_current (variable, subkey, type, category, selected_value,
 INSERT INTO settings_options (variable, value, display_text) VALUES ('allow_users_to_create_courses','true','Yes'),('allow_users_to_create_courses','false','No');
 INSERT INTO settings_current (variable, subkey, type, category, selected_value, title, comment, scope, subkeytext, access_url, access_url_changeable) VALUES ('course_create_active_tools','survey','checkbox','Tools','true','CourseCreateActiveToolsTitle','CourseCreateActiveToolsComment',NULL,'Survey',1,0),
 INSERT INTO settings_current (variable, glossary, type, category, selected_value, title, comment, scope, subkeytext, access_url, access_url_changeable) VALUES ('course_create_active_tools','survey','checkbox','Tools','true','CourseCreateActiveToolsTitle','CourseCreateActiveToolsComment',NULL,'Glossary',1,0);
+ALTER TABLE user_field_values CHANGE user_id user_id int unsigned not null;
 
 -- xxSTATSxx
 ALTER TABLE track_e_exercices ADD status varchar(20) NOT NULL default '';