diff --git a/config.inc.php b/config.inc.php
index 0673d7e..64b787f 100644
--- a/config.inc.php
+++ b/config.inc.php
@@ -920,6 +920,7 @@ function config_ensure_header(string $conf_dir, string $file, bool $force = fals
 
     $lines = file($file);
 
+    $is_success = false;
     $lines[0] = config_set_header($lines[0], $conf_id, $alias, $is_success);
     if(!$is_success)
       throw new Exception("Could not set header for '$file' in line: {$lines[0]}");