diff --git a/scripts/upgrade b/scripts/upgrade
index cfaafe3..18c5be6 100644
--- a/scripts/upgrade
+++ b/scripts/upgrade
@@ -109,7 +109,7 @@ fi
 ynh_script_progression --message="Updating a configuration file..." --weight=2
 
 # If password_hash doesn't exist, create it
-if [ -z "$password_hash" ]; then
+if [ -z "${password_hash:-}" ]; then
 	password_hash=$(echo $($install_dir/galene-password-generator $password))
 	ynh_app_setting_set --app=$app --key=password_hash --value="$password_hash"
 fi