diff --git a/apps/web/index.html b/apps/web/index.html
index 98ceba127..e2740c0ab 100644
--- a/apps/web/index.html
+++ b/apps/web/index.html
@@ -10,6 +10,19 @@
       src="https://analytics.thp.box/script.js"
       data-website-id="13760d0b-e30d-43c2-9026-1920a86720c8">
     </script>
+
+    <script>
+      // Restore clean URL when coming from 404 fallback (/?/route → /route)
+      (function(l) {
+        if (l.search && l.search.startsWith('?/')) {
+          var decoded = l.search.slice(2)
+            .split('&')
+            .map(function(s){ return s.replace(/~and~/g, '&') })
+            .join('?');
+          window.history.replaceState(null, null, '/' + decoded + l.hash);
+        }
+      })(window.location);
+    </script>
   </head>
   <body>
     <div id="root"></div>
diff --git a/apps/web/public/404.html b/apps/web/public/404.html
new file mode 100644
index 000000000..d7584cd5b
--- /dev/null
+++ b/apps/web/public/404.html
@@ -0,0 +1,22 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8" />
+    <title>Redirecting…</title>
+    <!-- SPA fallback for GitHub Pages using a custom domain at root -->
+    <script>
+      // Credits: https://github.com/rafgraph/spa-github-pages
+      (function() {
+        var l = window.location;
+        var segmentCount = 0; // custom domain served at root → keep 0
+        var redirect = l.protocol + '//' + l.hostname + (l.port ? ':' + l.port : '') +
+          l.pathname.split('/').slice(0, 1 + segmentCount).join('/') + '/?/' +
+          l.pathname.slice(1).split('/').slice(segmentCount).join('/').replace(/&/g, '~and~') +
+          (l.search ? '&' + l.search.slice(1).replace(/&/g, '~and~') : '') +
+          l.hash;
+        l.replace(redirect);
+      })();
+    </script>
+  </head>
+  <body></body>
+</html>
