diff --git a/src/Config/apexcharts.php b/src/Config/apexcharts.php
index c2a9158..5ffa9f8 100644
--- a/src/Config/apexcharts.php
+++ b/src/Config/apexcharts.php
@@ -51,7 +51,7 @@
         ],
 
         'subtitle' => [
-            'text' => 'undefined',
+            'text' => new \Balping\JsonRaw\Raw('undefined'),
             'align' => 'left',
         ],