diff --git a/dev/bots/service_worker_test.dart b/dev/bots/service_worker_test.dart
index 9dec42d0b1e8..2f4d3b0a78e8 100644
--- a/dev/bots/service_worker_test.dart
+++ b/dev/bots/service_worker_test.dart
@@ -21,9 +21,11 @@ final String _testAppWebDirectory = path.join(_testAppDirectory, 'web');
 final String _appBuildDirectory = path.join(_testAppDirectory, 'build', 'web');
 final String _target = path.join('lib', 'service_worker_test.dart');
 final String _targetWithCachedResources = path.join('lib', 'service_worker_test_cached_resources.dart');
+final String _targetWithBlockedServiceWorkers = path.join('lib', 'service_worker_test_blocked_service_workers.dart');
 final String _targetPath = path.join(_testAppDirectory, _target);
 
 enum ServiceWorkerTestType {
+  blockedServiceWorkers,
   withoutFlutterJs,
   withFlutterJs,
   withFlutterJsShort,
@@ -37,6 +39,7 @@ Future<void> main() async {
   await runWebServiceWorkerTestWithCachingResources(headless: false, testType: ServiceWorkerTestType.withoutFlutterJs);
   await runWebServiceWorkerTestWithCachingResources(headless: false, testType: ServiceWorkerTestType.withFlutterJs);
   await runWebServiceWorkerTestWithCachingResources(headless: false, testType: ServiceWorkerTestType.withFlutterJsShort);
+  await runWebServiceWorkerTestWithBlockedServiceWorkers(headless: false);
 }
 
 Future<void> _setAppVersion(int version) async {
@@ -52,6 +55,9 @@ Future<void> _setAppVersion(int version) async {
 String _testTypeToIndexFile(ServiceWorkerTestType type) {
   late String indexFile;
   switch (type) {
+    case ServiceWorkerTestType.blockedServiceWorkers:
+      indexFile = 'index_with_blocked_service_workers.html';
+      break;
     case ServiceWorkerTestType.withFlutterJs:
       indexFile = 'index_with_flutterjs.html';
       break;
@@ -562,3 +568,89 @@ Future<void> runWebServiceWorkerTestWithCachingResources({
 
   print('END runWebServiceWorkerTestWithCachingResources(headless: $headless, testType: $testType)\n');
 }
+
+Future<void> runWebServiceWorkerTestWithBlockedServiceWorkers({
+  required bool headless
+}) async {
+  final Map<String, int> requestedPathCounts = <String, int>{};
+  void expectRequestCounts(Map<String, int> expectedCounts) =>
+      _expectRequestCounts(expectedCounts, requestedPathCounts);
+
+  AppServer? server;
+  Future<void> waitForAppToLoad(Map<String, int> waitForCounts) async =>
+      _waitForAppToLoad(waitForCounts, requestedPathCounts, server);
+
+  Future<void> startAppServer({
+    required String cacheControl,
+  }) async {
+    final int serverPort = await findAvailablePort();
+    final int browserDebugPort = await findAvailablePort();
+    server = await AppServer.start(
+      headless: headless,
+      cacheControl: cacheControl,
+      // TODO(yjbanov): use a better port disambiguation strategy than trying
+      //                to guess what ports other tests use.
+      appUrl: 'http://localhost:$serverPort/index.html',
+      serverPort: serverPort,
+      browserDebugPort: browserDebugPort,
+      appDirectory: _appBuildDirectory,
+      additionalRequestHandlers: <Handler>[
+        (Request request) {
+          final String requestedPath = request.url.path;
+          requestedPathCounts.putIfAbsent(requestedPath, () => 0);
+          requestedPathCounts[requestedPath] = requestedPathCounts[requestedPath]! + 1;
+          if (requestedPath == 'CLOSE') {
+            return Response.ok('OK');
+          }
+          return Response.notFound('');
+        },
+      ],
+    );
+  }
+
+  // Preserve old index.html as index_og.html so we can restore it later for other tests
+  await runCommand(
+    'mv',
+    <String>[
+      'index.html',
+      'index_og.html',
+    ],
+    workingDirectory: _testAppWebDirectory,
+  );
+
+  print('BEGIN runWebServiceWorkerTestWithBlockedServiceWorkers(headless: $headless)\n');
+  try {
+    await _rebuildApp(version: 1, testType: ServiceWorkerTestType.blockedServiceWorkers, target: _targetWithBlockedServiceWorkers);
+
+    print('Ensure app starts (when service workers are blocked)');
+    await startAppServer(cacheControl: 'max-age=3600');
+    await waitForAppToLoad(<String, int>{
+      'CLOSE': 1,
+    });
+    expectRequestCounts(<String, int>{
+      'index.html': 1,
+      'flutter.js': 1,
+      'main.dart.js': 1,
+      'assets/FontManifest.json': 1,
+      'assets/fonts/MaterialIcons-Regular.otf': 1,
+      'CLOSE': 1,
+      // In headless mode Chrome does not load 'manifest.json' and 'favicon.ico'.
+      if (!headless)
+        ...<String, int>{
+          'manifest.json': 1,
+          'favicon.ico': 1,
+        },
+    });
+  } finally {
+    await runCommand(
+      'mv',
+      <String>[
+        'index_og.html',
+        'index.html',
+      ],
+      workingDirectory: _testAppWebDirectory,
+    );
+    await server?.stop();
+  }
+  print('END runWebServiceWorkerTestWithBlockedServiceWorkers(headless: $headless)\n');
+}
diff --git a/dev/bots/test.dart b/dev/bots/test.dart
index 47b7d5331629..224d83501024 100644
--- a/dev/bots/test.dart
+++ b/dev/bots/test.dart
@@ -1087,6 +1087,7 @@ Future<void> _runWebLongRunningTests() async {
     () => runWebServiceWorkerTestWithCachingResources(headless: true, testType: ServiceWorkerTestType.withoutFlutterJs),
     () => runWebServiceWorkerTestWithCachingResources(headless: true, testType: ServiceWorkerTestType.withFlutterJs),
     () => runWebServiceWorkerTestWithCachingResources(headless: true, testType: ServiceWorkerTestType.withFlutterJsShort),
+    () => runWebServiceWorkerTestWithBlockedServiceWorkers(headless: true),
     () => _runWebStackTraceTest('profile', 'lib/stack_trace.dart'),
     () => _runWebStackTraceTest('release', 'lib/stack_trace.dart'),
     () => _runWebStackTraceTest('profile', 'lib/framework_stack_trace.dart'),
diff --git a/dev/integration_tests/web/lib/service_worker_test_blocked_service_workers.dart b/dev/integration_tests/web/lib/service_worker_test_blocked_service_workers.dart
new file mode 100644
index 000000000000..f7c7e9129576
--- /dev/null
+++ b/dev/integration_tests/web/lib/service_worker_test_blocked_service_workers.dart
@@ -0,0 +1,10 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:html' as html;
+Future<void> main() async {
+  const String response = 'CLOSE?version=1';
+  await html.HttpRequest.getString(response);
+  html.document.body?.appendHtml(response);
+}
diff --git a/dev/integration_tests/web/web/index_with_blocked_service_workers.html b/dev/integration_tests/web/web/index_with_blocked_service_workers.html
new file mode 100644
index 000000000000..c590fdbd0a2d
--- /dev/null
+++ b/dev/integration_tests/web/web/index_with_blocked_service_workers.html
@@ -0,0 +1,48 @@
+<!DOCTYPE HTML>
+<!-- Copyright 2014 The Flutter Authors. All rights reserved.
+Use of this source code is governed by a BSD-style license that can be
+found in the LICENSE file. -->
+<html>
+<head>
+  <meta charset="UTF-8">
+  <meta content="IE=Edge" http-equiv="X-UA-Compatible">
+
+  <title>Web Test</title>
+  <!-- iOS meta tags & icons -->
+  <meta name="apple-mobile-web-app-capable" content="yes">
+  <meta name="apple-mobile-web-app-status-bar-style" content="black">
+  <meta name="apple-mobile-web-app-title" content="Web Test">
+  <link rel="manifest" href="manifest.json">
+
+  <script>
+    // This is to break the serviceWorker registration, and make it throw a DOMException!
+    // Test for issue https://github.com/flutter/flutter/issues/103972
+    window.navigator.serviceWorker.register = (url) => {
+      console.error('Failed to register/update a ServiceWorker for scope ', url,
+          ': Storage access is restricted in this context due to user settings or private browsing mode.');
+      return Promise.reject(new DOMException('The operation is insecure.'));
+    }
+  </script>
+
+  <script>
+    // The value below is injected by flutter build, do not touch.
+    var serviceWorkerVersion = null;
+  </script>
+  <!-- This script adds the flutter initialization JS code -->
+  <script src="flutter.js" defer></script>
+</head>
+<body>
+  <script>
+    window.addEventListener('load', function(ev) {
+      // Download main.dart.js
+      _flutter.loader.loadEntrypoint({
+        serviceWorker: {
+          serviceWorkerVersion: serviceWorkerVersion,
+        }
+      }).then(function(engineInitializer) {
+        return engineInitializer.autoStart();
+      });
+    });
+  </script>
+</body>
+</html>
diff --git a/packages/flutter_tools/lib/src/web/file_generators/flutter_js.dart b/packages/flutter_tools/lib/src/web/file_generators/flutter_js.dart
index 6a5f761087e8..257cb42d3918 100644
--- a/packages/flutter_tools/lib/src/web/file_generators/flutter_js.dart
+++ b/packages/flutter_tools/lib/src/web/file_generators/flutter_js.dart
@@ -76,6 +76,7 @@ _flutter.loader = null;
 
     _loadEntrypoint(entrypointUrl) {
       if (!this._scriptLoaded) {
+        console.debug("Injecting <script> tag.");
         this._scriptLoaded = new Promise((resolve, reject) => {
           let scriptTag = document.createElement("script");
           scriptTag.src = entrypointUrl;
@@ -96,7 +97,7 @@ _flutter.loader = null;
     _waitForServiceWorkerActivation(serviceWorker, entrypointUrl) {
       if (!serviceWorker || serviceWorker.state == "activated") {
         if (!serviceWorker) {
-          console.warn("Cannot activate a null service worker. Falling back to plain <script> tag.");
+          console.warn("Cannot activate a null service worker.");
         } else {
           console.debug("Service worker already active.");
         }
@@ -114,7 +115,7 @@ _flutter.loader = null;
 
     _loadWithServiceWorker(entrypointUrl, serviceWorkerOptions) {
       if (!("serviceWorker" in navigator) || serviceWorkerOptions == null) {
-        console.warn("Service worker not supported (or configured). Falling back to plain <script> tag.", serviceWorkerOptions);
+        console.warn("Service worker not supported (or configured).", serviceWorkerOptions);
         return this._loadEntrypoint(entrypointUrl);
       }
 
@@ -145,6 +146,11 @@ _flutter.loader = null;
               console.debug("Loading app from service worker.");
               return this._loadEntrypoint(entrypointUrl);
             }
+          })
+          .catch((error) => {
+            // Some exception happened while registering/activating the service worker.
+            console.warn("Failed to register or activate service worker:", error);
+            return this._loadEntrypoint(entrypointUrl);
           });
 
       // Timeout race promise
@@ -153,7 +159,7 @@ _flutter.loader = null;
         timeout = new Promise((resolve, _) => {
           setTimeout(() => {
             if (!this._scriptLoaded) {
-              console.warn("Failed to load app from service worker. Falling back to plain <script> tag.");
+              console.warn("Loading from service worker timed out after", timeoutMillis, "milliseconds.");
               resolve(this._loadEntrypoint(entrypointUrl));
             }
           }, timeoutMillis);