diff --git a/web/cloudflare-worker/README.md b/web/cloudflare-worker/README.md
index c2cd4be84b00..e4497ab23cb5 100644
--- a/web/cloudflare-worker/README.md
+++ b/web/cloudflare-worker/README.md
@@ -14,7 +14,7 @@ Every request runs the Worker first (`run_worker_first: true`), which reads the
 | HTML (`/`, `/index.html`, any SPA deep link) | Each `<script nonce="nonce-random-value">` gets a per-request nonce that matches the CSP. `Cache-Control: no-cache`, with no `ETag` or `Last-Modified`, since a 304 would pair a cached body with a new nonce |
 | Content-hashed files (`main-<16 hex>.bundle.js`, `name.<10 hex>.css`) | `Cache-Control: public, max-age=31536000, immutable` |
 | Files with fixed names (`version.json`, `service-worker.js`, `manifest.json`, ...) | Default `public, max-age=0, must-revalidate`, with an `ETag` |
-| A file the current build doesn't have (`/main-<old hash>.bundle.js`) | The file from a previous build, if the environment has a `PREVIOUS_BUILDS` bucket that holds it (see [Files from previous builds](#files-from-previous-builds)). Otherwise `404`, so a stale tab gets a `ChunkLoadError` and recovers instead of parsing HTML as JavaScript |
+| A file the current build doesn't have (`/main-<old hash>.bundle.js`) | The file from a previous build, if the environment has a `PREVIOUS_BUILDS` bucket that holds it (see [Files from previous builds](#files-from-previous-builds)). Otherwise `404`, also when the bucket can't be read, so a stale tab gets a `ChunkLoadError` and recovers instead of parsing HTML as JavaScript |
 | Any other path that does not exist (`/r/123`) | The app shell (`index.html`) with `200` |
 | `/.well-known/apple-app-site-association` and `/apple-app-site-association` | The same file with `Content-Type: application/json` |
 
diff --git a/web/cloudflare-worker/src/index.ts b/web/cloudflare-worker/src/index.ts
index 605990253d84..e501b582d93b 100644
--- a/web/cloudflare-worker/src/index.ts
+++ b/web/cloudflare-worker/src/index.ts
@@ -71,13 +71,19 @@ async function getPreviousBuildFile(env: Env, url: URL, method: string): Promise
         return null;
     }
 
-    if (method === 'HEAD') {
-        const object = await env.PREVIOUS_BUILDS.head(key);
-        return object ? new Response(null, {headers: getPreviousBuildFileHeaders(object)}) : null;
-    }
+    try {
+        if (method === 'HEAD') {
+            const object = await env.PREVIOUS_BUILDS.head(key);
+            return object ? new Response(null, {headers: getPreviousBuildFileHeaders(object)}) : null;
+        }
 
-    const object = await env.PREVIOUS_BUILDS.get(key);
-    return object ? new Response(object.body, {headers: getPreviousBuildFileHeaders(object)}) : null;
+        const object = await env.PREVIOUS_BUILDS.get(key);
+        return object ? new Response(object.body, {headers: getPreviousBuildFileHeaders(object)}) : null;
+    } catch (error) {
+        // A 404 lets the tab recover with a reload, as it does for a file no build has.
+        console.error(`Failed to read ${key} from the previous builds bucket`, error);
+        return null;
+    }
 }
 
 export default {
diff --git a/web/cloudflare-worker/tests/worker.test.ts b/web/cloudflare-worker/tests/worker.test.ts
index 09997a2c11b4..187bbe92050e 100644
--- a/web/cloudflare-worker/tests/worker.test.ts
+++ b/web/cloudflare-worker/tests/worker.test.ts
@@ -260,6 +260,18 @@ describe('staging worker with files from previous builds', () => {
         assert.equal(await response.text(), '');
     });
 
+    test('returns 404 when the previous builds bucket fails', async () => {
+        // Given a chunk path whose bucket lookup fails (R2 rejects keys over 1,024 bytes)
+        for (const method of ['GET', 'HEAD']) {
+            // When it is requested
+            const response = await server.fetch(`/${'a'.repeat(1100)}.bundle.js`, {method});
+
+            // Then the Worker answers as it does for a chunk no build has, instead of throwing
+            assert.equal(response.status, 404, method);
+            assertSecurityHeaders(response);
+        }
+    });
+
     test('serves the current build when a previous build has the same file', async () => {
         // Given a file that is in both the current build and the bucket
         // When it is requested