diff --git a/scripts/upgrade b/scripts/upgrade
index bbf006c..28dce37 100644
--- a/scripts/upgrade
+++ b/scripts/upgrade
@@ -23,7 +23,7 @@ upgrade_type=$(ynh_check_app_version_changed)
 ynh_script_progression --message="Ensuring downward compatibility..." --weight=1
 
 # If language doesn't exist, create it
-if [ -z "$language" ]; then
+if [ -z "${language:-}" ]; then
 	language="en-US"
 	ynh_app_setting_set --app=$app --key=language --value=$language
 fi