diff --git a/astro.config.mjs b/astro.config.mjs
index 716ad0a..dad198a 100644
--- a/astro.config.mjs
+++ b/astro.config.mjs
@@ -170,6 +170,11 @@ export default defineConfig({
         cleanupOutdatedCaches: true,
         clientsClaim: true,
         skipWaiting: true,
+        // No SPA fallback. The default answers EVERY navigation it has not
+        // precached with the cached front page, so /tarballz/ (served by nginx
+        // outside the Astro build) and unknown URLs showed the home page instead
+        // of the real page or the 404. Every Astro page is precached anyway.
+        navigateFallback: null,
       },
       devOptions: { enabled: false },
     }),