diff --git a/BookReaderDemo/demo-iiif.html b/BookReaderDemo/demo-iiif.html
index 899965745..6799c670e 100644
--- a/BookReaderDemo/demo-iiif.html
+++ b/BookReaderDemo/demo-iiif.html
@@ -5,6 +5,7 @@
     <meta name="apple-mobile-web-app-capable" content="yes">
 
     <!-- WC dependencies -->
+    <script type="text/javascript" src="https://cdnjs.cloudflare.com/polyfill/v3/polyfill.min.js?features=es2015%2Ces5%2CglobalThis"></script>
     <script type="text/javascript" src="https://unpkg.com/lit@2.1.2/polyfill-support.js"></script>
     <script type="text/javascript" src="https://unpkg.com/@webcomponents/webcomponentsjs@2.2.10/webcomponents-bundle.js"></script>
 
diff --git a/BookReaderDemo/demo-internetarchive.html b/BookReaderDemo/demo-internetarchive.html
index 6c6f84330..c9c1a51ad 100644
--- a/BookReaderDemo/demo-internetarchive.html
+++ b/BookReaderDemo/demo-internetarchive.html
@@ -8,6 +8,7 @@
     <meta name="apple-mobile-web-app-capable" content="yes">
 
     <!-- WC dependencies -->
+    <script type="text/javascript" src="https://cdnjs.cloudflare.com/polyfill/v3/polyfill.min.js?features=es2015%2Ces5%2CglobalThis"></script>
     <script type="text/javascript" src="https://unpkg.com/lit@2.1.2/polyfill-support.js"></script>
     <script type="text/javascript" src="https://unpkg.com/@webcomponents/webcomponentsjs@2.2.10/webcomponents-bundle.js"></script>