diff --git a/packages/service-worker/worker/src/driver.ts b/packages/service-worker/worker/src/driver.ts
index b4e046539f..19fc0dded6 100644
--- a/packages/service-worker/worker/src/driver.ts
+++ b/packages/service-worker/worker/src/driver.ts
@@ -607,16 +607,22 @@ export class Driver implements Debuggable, UpdateSource {
 
   /**
    * Retrieve a copy of the latest manifest from the server.
+   * Return `null` if `ignoreOfflineError` is true (default: false) and the server or client are
+   * offline (detected as response status 504).
    */
-  private async fetchLatestManifest(): Promise<Manifest> {
+  private async fetchLatestManifest(ignoreOfflineError?: false): Promise<Manifest>;
+  private async fetchLatestManifest(ignoreOfflineError: true): Promise<Manifest | null>;
+  private async fetchLatestManifest(ignoreOfflineError = false): Promise<Manifest | null> {
     const res =
         await this.safeFetch(this.adapter.newRequest('ngsw.json?ngsw-cache-bust=' + Math.random()));
     if (!res.ok) {
       if (res.status === 404) {
         await this.deleteAllCaches();
         await this.scope.registration.unregister();
+      } else if (res.status === 504 && ignoreOfflineError) {
+        return null;
       }
-      throw new Error('Manifest fetch failed!');
+      throw new Error(`Manifest fetch failed! (status: ${res.status})`);
     }
     this.lastUpdateCheck = this.adapter.time;
     return res.json();
@@ -728,7 +734,15 @@ export class Driver implements Debuggable, UpdateSource {
   async checkForUpdate(): Promise<boolean> {
     let hash: string = '(unknown)';
     try {
-      const manifest = await this.fetchLatestManifest();
+      const manifest = await this.fetchLatestManifest(true);
+
+      if (manifest === null) {
+        // Client or server offline. Unable to check for updates at this time.
+        // Continue to service clients (existing and new).
+        this.debugger.log('Check for update aborted. (Client or server offline.)');
+        return false;
+      }
+
       hash = hashManifest(manifest);
 
       // Check whether this is really an update.
@@ -972,4 +986,4 @@ function errorToString(error: any): string {
   } else {
     return `${error}`;
   }
-}
\ No newline at end of file
+}
diff --git a/packages/service-worker/worker/test/happy_spec.ts b/packages/service-worker/worker/test/happy_spec.ts
index 2a63385850..f560394805 100644
--- a/packages/service-worker/worker/test/happy_spec.ts
+++ b/packages/service-worker/worker/test/happy_spec.ts
@@ -516,6 +516,17 @@ const manifestUpdateHash = sha1(JSON.stringify(manifestUpdate));
       expect(await scope.caches.keys()).toEqual([]);
     });
 
+    async_it('does not unregister or change state when offline (i.e. manifest 504s)', async() => {
+      expect(await makeRequest(scope, '/foo.txt')).toEqual('this is foo');
+      await driver.initialized;
+      server.online = false;
+
+      expect(await driver.checkForUpdate()).toEqual(false);
+      expect(driver.state).toEqual(DriverReadyState.NORMAL);
+      expect(scope.unregistered).toBeFalsy();
+      expect(await scope.caches.keys()).not.toEqual([]);
+    });
+
     describe('unhashed requests', () => {
       async_beforeEach(async() => {
         expect(await makeRequest(scope, '/foo.txt')).toEqual('this is foo');
diff --git a/packages/service-worker/worker/testing/mock.ts b/packages/service-worker/worker/testing/mock.ts
index 4ab6502464..208e75f9ad 100644
--- a/packages/service-worker/worker/testing/mock.ts
+++ b/packages/service-worker/worker/testing/mock.ts
@@ -96,6 +96,7 @@ export class MockServerState {
   private gate: Promise<void> = Promise.resolve();
   private resolve: Function|null = null;
   private resolveNextRequest: Function;
+  online = true;
   nextRequest: Promise<Request>;
 
   constructor(private resources: Map<string, Response>, private errors: Set<string>) {
@@ -108,6 +109,10 @@ export class MockServerState {
 
     await this.gate;
 
+    if (!this.online) {
+      throw new Error('Offline.');
+    }
+
     if (req.credentials === 'include') {
       return new MockResponse(null, {status: 0, statusText: '', type: 'opaque'});
     }
@@ -171,6 +176,7 @@ export class MockServerState {
     this.nextRequest = new Promise(resolve => { this.resolveNextRequest = resolve; });
     this.gate = Promise.resolve();
     this.resolve = null;
+    this.online = true;
   }
 }