diff --git a/.gitignore b/.gitignore
index b073caed..3e4dfeb3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -26,3 +26,5 @@ website/node_modules
 website/i18n/*
 website/static/static/katex.*
 website/static/static/fonts
+website/static/static/copy-tex.*
+website/static/static/mhchem.*
diff --git a/website/lib/build.js b/website/lib/build.js
index 3366edfc..1b6482e0 100644
--- a/website/lib/build.js
+++ b/website/lib/build.js
@@ -16,11 +16,20 @@ fs.copySync('../dist/katex.min.js', 'static/static/katex.min.js');
 fs.copySync('../dist/katex.min.css', 'static/static/katex.min.css');
 fs.copySync('../dist/fonts', 'static/static/fonts');
 
+// copy local built KaTeX extensions
+fs.copySync('../dist/contrib/copy-tex.min.css', 'static/static/copy-tex.min.css');
+fs.copySync('../dist/contrib/copy-tex.min.js', 'static/static/copy-tex.min.js');
+fs.copySync('../dist/contrib/mhchem.min.js', 'static/static/mhchem.min.js');
+
+
 // use KaTeX from CDN on the main page for Netlify production deploy
 if (process.env.CONTEXT === 'production') {
     const version = require('../versions.json')[0];
     let indexHtml = fs.readFileSync('pages/index.html', 'utf8');
     indexHtml = indexHtml.replace(/(["'])static\/(katex|fonts)/g,
         `$1https://cdn.jsdelivr.net/npm/katex@${version}/dist/$2`);
+    // the CDN pathway is different for `copy-tex` and `mhchem`
+    indexHtml = indexHtml.replace(/(["'])static\/(copy-tex|mhchem)/g,
+            `$1https://cdn.jsdelivr.net/npm/katex@${version}/dist/contrib/$2`);
     fs.writeFileSync('pages/index.html', indexHtml);
 }
diff --git a/website/pages/index.html b/website/pages/index.html
index 73bdf9c8..13c39ee3 100644
--- a/website/pages/index.html
+++ b/website/pages/index.html
@@ -24,9 +24,12 @@
     <link rel="stylesheet" href="https://fonts.googleapis.com/css?family=Lato:300,400,700,700i">
     <link rel="stylesheet" href="static/katex.min.css" crossorigin="anonymous">
     <link rel="stylesheet" href="static/index.css">
+    <link rel="stylesheet" href="static/copy-tex.min.css" crossorigin="anonymous">
 
     <script defer src="https://cdn.jsdelivr.net/npm/clipboard@2.0.1/dist/clipboard.min.js" integrity="sha256-hIvIxeqhGZF+VVeM55k0mJvWpQ6gTkWk3Emc+NmowYA=" crossorigin="anonymous"></script>
     <script defer src="static/katex.min.js" crossorigin="anonymous"></script>
+    <script defer src="static/mhchem.min.js" crossorigin="anonymous"></script>
+    <script defer src="static/copy-tex.min.js" crossorigin="anonymous"></script>
     <script defer src="js/index.js" type="text/javascript"></script>
     <script defer src="https://cdn.jsdelivr.net/npm/webfontloader@1.6.28/webfontloader.js" integrity="sha256-4O4pS1SH31ZqrSO2A/2QJTVjTPqVe+jnYgOWUVr7EEc=" crossorigin="anonymous"></script>
   </head>