diff --git a/public/sw.js b/public/sw.js
index edc756a..6e8f608 100644
--- a/public/sw.js
+++ b/public/sw.js
@@ -59,7 +59,9 @@ async function cacheFirst(req) {
     const hit = await cache.match(req);
     if (hit) return hit;
     const res = await fetch(req);
-    if (res && res.ok) cache.put(req, res.clone());
+    // Await the write: respondWith() keeps the worker alive for this promise, so the asset is
+    // actually persisted before the worker can be terminated (otherwise offline use loses it).
+    if (res && res.ok) await cache.put(req, res.clone());
     return res;
 }