diff --git a/scripts/upgrade b/scripts/upgrade
index a9beb78..4becbd5 100644
--- a/scripts/upgrade
+++ b/scripts/upgrade
@@ -57,7 +57,7 @@ if [ -z "$phpversion" ]; then
 fi
 
 # If custom_error_files doesn't exist, create it. We assume it is the default system one.
-if [ -n "$(ynh_app_setting_get --app=$app --key=custom_error_file)" ]; then
+if [ -z "$custom_error_file" ]; then
 	custom_error_file=$(ynh_app_setting_get --app=$app --key=custom_error_file)
 fi