diff --git a/web_gui/gui_v3/customjs/param.php b/web_gui/gui_v3/customjs/param.php
index 79fb6d0c7..366f13aa2 100644
--- a/web_gui/gui_v3/customjs/param.php
+++ b/web_gui/gui_v3/customjs/param.php
@@ -14,6 +14,8 @@
 include("../common.php");
 include("../plugin.php");
 
+header('Content-Type: application/javascript');
+
 foreach($CHARTJS as $conf => $val)
 {
         echo "$conf=$val;\n";