diff --git a/server/server.js b/server/server.js
index f28b21b..50e6d3a 100644
--- a/server/server.js
+++ b/server/server.js
@@ -1576,7 +1576,13 @@ app.get('/api/download/:videoId/prepare', async (c) => {
   if (ready) {
     if (!servableTo(ready, hevcOk)) return c.json({ ok: true, state: 'legacy', reason: 'hevc' }, 200, nocache);
     media.touch(videoId);
-    return c.json({ ok: true, state: 'ready', gen: ready.gen, size: ready.size, sha256: ready.sha256 || null,
+    // The row's size can differ from the mp4 on disk (it is not the file the
+    // device fetches byte-for-byte), so report the file's real length.
+    const path = await media.filePath(videoId, ready.gen);
+    let size = 0;
+    try { size = path ? Bun.file(path).size : 0; } catch { /* vanished */ }
+    if (!size) return c.json({ ok: true, state: 'legacy', reason: 'cached file unavailable' }, 200, nocache);
+    return c.json({ ok: true, state: 'ready', gen: ready.gen, size, sha256: ready.sha256 || null,
       etag: `"${videoId}.${ready.gen}"`, ext: 'mp4' }, 200, nocache);
   }
   // A job refused moments ago (too long for the cache, cache offline…) would