diff --git a/source/get-started/index.html.md.erb b/source/get-started/index.html.md.erb
index 34b26721..cd49ab03 100644
--- a/source/get-started/index.html.md.erb
+++ b/source/get-started/index.html.md.erb
@@ -67,7 +67,7 @@ In your live application, we recommend [using an automated task or your build pi
 1. Add the following to the top of the `<body class="govuk-template__body">` section of your page template:
 
     ```html
-    <script>document.body.className = ((document.body.className) ? document.body.className + ' js-enabled' : 'js-enabled');</script>
+    <script>document.body.className += ' js-enabled' + ('noModule' in HTMLScriptElement.prototype ? ' govuk-frontend-supported' : '');</script>
     ```
 
 2. Copy the `/node-modules/govuk-frontend/dist/govuk/govuk-frontend.min.js` file into your application.
diff --git a/source/install-using-precompiled-files/index.html.md.erb b/source/install-using-precompiled-files/index.html.md.erb
index e2e1514a..562ff99e 100644
--- a/source/install-using-precompiled-files/index.html.md.erb
+++ b/source/install-using-precompiled-files/index.html.md.erb
@@ -45,9 +45,7 @@ You’ll not be able to:
         <![endif]-->
       </head>
       <body class="govuk-template__body">
-        <script>
-          document.body.className = ((document.body.className) ? document.body.className + ' js-enabled' : 'js-enabled');
-        </script>
+        <script>document.body.className += ' js-enabled' + ('noModule' in HTMLScriptElement.prototype ? ' govuk-frontend-supported' : '');</script>
         <!-- component HTML -->
         <script src="/javascripts/govuk-frontend-<VERSION-NUMBER>.min.js"></script>
         <script>
