diff --git a/scripts/upgrade b/scripts/upgrade
index 50fd819..7fbec63 100644
--- a/scripts/upgrade
+++ b/scripts/upgrade
@@ -29,17 +29,17 @@ ynh_systemd_action --service_name=$app --action=stop --log_path=systemd
 #=================================================
 ynh_script_progression --message="Ensuring downward compatibility..." --weight=1
 
-if [ -z "$registration_enabled" ]; then
+if [ -z "${registration_enabled:-}" ]; then
 	registration_enabled="true"
 	ynh_app_setting_set --app=$app --key=registration_enabled --value=$registration_enabled
 fi
 
-if [ -z "$login_enabled" ]; then
+if [ -z "${login_enabled:-}" ]; then
 	login_enabled="true"
 	ynh_app_setting_set --app=$app --key=login_enabled --value=$login_enabled
 fi
 
-if [ -z "$captcha_enabled" ]; then
+if [ -z "${captcha_enabled:-}" ]; then
 	captcha_enabled="true"
 	ynh_app_setting_set --app=$app --key=captcha_enabled --value=$captcha_enabled
 fi