diff --git a/packages/service-worker/worker/src/app-version.ts b/packages/service-worker/worker/src/app-version.ts
index 1329c9aaf4..dafdcabfe0 100644
--- a/packages/service-worker/worker/src/app-version.ts
+++ b/packages/service-worker/worker/src/app-version.ts
@@ -15,6 +15,12 @@ import {IdleScheduler} from './idle';
 import {Manifest} from './manifest';
 
 
+const BACKWARDS_COMPATIBILITY_NAVIGATION_URLS = [
+  {positive: true, regex: '^/.*$'},
+  {positive: false, regex: '^/.*\\.[^/]*$'},
+  {positive: false, regex: '^/.*__'},
+];
+
 /**
  * A specific version of the application, identified by a unique manifest
  * as determined by its hash.
@@ -85,6 +91,10 @@ export class AppVersion implements UpdateSource {
                                   this.scope, this.adapter, config, this.database,
                                   `ngsw:${config.version}:data`));
 
+    // This keeps backwards compatibility with app versions without navigation urls.
+    // Fix: https://github.com/angular/angular/issues/27209
+    manifest.navigationUrls = manifest.navigationUrls || BACKWARDS_COMPATIBILITY_NAVIGATION_URLS;
+
     // Create `include`/`exclude` RegExps for the `navigationUrls` declared in the manifest.
     const includeUrls = manifest.navigationUrls.filter(spec => spec.positive);
     const excludeUrls = manifest.navigationUrls.filter(spec => !spec.positive);
diff --git a/packages/service-worker/worker/test/happy_spec.ts b/packages/service-worker/worker/test/happy_spec.ts
index d1278434bf..a4fba8680a 100644
--- a/packages/service-worker/worker/test/happy_spec.ts
+++ b/packages/service-worker/worker/test/happy_spec.ts
@@ -9,7 +9,7 @@
 import {processNavigationUrls} from '../../config/src/generator';
 import {CacheDatabase} from '../src/db-cache';
 import {Driver, DriverReadyState} from '../src/driver';
-import {Manifest} from '../src/manifest';
+import {AssetGroupConfig, DataGroupConfig, Manifest} from '../src/manifest';
 import {sha1} from '../src/sha1';
 import {MockCache, clearAllCaches} from '../testing/cache';
 import {MockRequest} from '../testing/fetch';
@@ -66,6 +66,24 @@ const brokenManifest: Manifest = {
   hashTable: tmpHashTableForFs(brokenFs, {'/foo.txt': true}),
 };
 
+// Manifest without navigation urls to test backward compatibility with
+// versions < 6.0.0.
+export interface ManifestV5 {
+  configVersion: number;
+  appData?: {[key: string]: string};
+  index: string;
+  assetGroups?: AssetGroupConfig[];
+  dataGroups?: DataGroupConfig[];
+  hashTable: {[url: string]: string};
+}
+
+// To simulate versions < 6.0.0
+const manifestOld: ManifestV5 = {
+  configVersion: 1,
+  index: '/foo.txt',
+  hashTable: tmpHashTableForFs(dist),
+};
+
 const manifest: Manifest = {
   configVersion: 1,
   appData: {
@@ -989,6 +1007,28 @@ const manifestUpdateHash = sha1(JSON.stringify(manifestUpdate));
         expect(await requestFoo('only-if-cached', 'same-origin')).toBe('this is foo');
         expect(await requestFoo('only-if-cached', 'no-cors')).toBeNull();
       });
+
+      describe('Backwards compatibility with v5', () => {
+        beforeEach(() => {
+          const serverV5 = new MockServerStateBuilder()
+                               .withStaticFiles(dist)
+                               .withManifest(<Manifest>manifestOld)
+                               .build();
+
+          scope = new SwTestHarnessBuilder().withServerState(serverV5).build();
+          driver = new Driver(scope, scope, new CacheDatabase(scope, scope));
+        });
+
+        // Test this bug: https://github.com/angular/angular/issues/27209
+        async_it(
+            'Fill previous versions of manifests with default navigation urls for backwards compatibility',
+            async() => {
+              expect(await makeRequest(scope, '/foo.txt')).toEqual('this is foo');
+              await driver.initialized;
+              scope.updateServerState(serverUpdate);
+              expect(await driver.checkForUpdate()).toEqual(true);
+            });
+      });
     });
   });
 })();