diff --git a/packages/google_sign_in/google_sign_in_web/CHANGELOG.md b/packages/google_sign_in/google_sign_in_web/CHANGELOG.md
index a41ce367d9bd..62e3299f0eca 100644
--- a/packages/google_sign_in/google_sign_in_web/CHANGELOG.md
+++ b/packages/google_sign_in/google_sign_in_web/CHANGELOG.md
@@ -1,3 +1,10 @@
+## 0.8.3
+
+* Fix initialization error that causes https://github.com/flutter/flutter/issues/48527
+* Throw a PlatformException when there's an initialization problem (like wrong server-side config).
+* Throw a StateError when checking .initialized before calling .init()
+* Update setup instructions in the README.
+
 ## 0.8.2+1
 
 * Add a non-op Android implementation to avoid a flaky Gradle issue.
diff --git a/packages/google_sign_in/google_sign_in_web/README.md b/packages/google_sign_in/google_sign_in_web/README.md
index 182b21018aa4..599a49372aa5 100644
--- a/packages/google_sign_in/google_sign_in_web/README.md
+++ b/packages/google_sign_in/google_sign_in_web/README.md
@@ -5,18 +5,16 @@ The web implementation of [google_sign_in](https://pub.dev/google_sign_in/google
 ## Usage
 
 ### Import the package
-To use this plugin, follow the [plugin installation instructions](https://pub.dartlang.org/packages/google_sign_in#pub-pkg-tab-installing).
 
-Remember that for web plugins you need to depend both on the "native" version that provides the Dart interface that you'll use in your app), and the "web" version, that provides the implementation of the plugin for the web platform.
+This package is the endorsed implementation of `google_sign_in` for the web platform since version `4.1.0`, so it gets automatically added to your dependencies by depending on `google_sign_in: ^4.1.0`.
 
-This is what the above means to your `pubspec.yaml`:
+No modifications to your pubspec.yaml should be required in a recent enough version of Flutter (`>=1.12.13+hotfix.4`):
 
-```
+```yaml
 ...
 dependencies:
   ...
-  google_sign_in: ^4.0.14
-  google_sign_in_web: ^0.8.0
+  google_sign_in: ^4.1.0
   ...
 ...
 ```
@@ -28,8 +26,8 @@ First, go through the instructions [here](https://developers.google.com/identity
 On your `web/index.html` file, add the following `meta` tag, somewhere in the
 `head` of the document:
 
-```
-  <meta name="google-signin-client_id" content="YOUR_GOOGLE_SIGN_IN_OAUTH_CLIENT_ID.apps.googleusercontent.com">
+```html
+<meta name="google-signin-client_id" content="YOUR_GOOGLE_SIGN_IN_OAUTH_CLIENT_ID.apps.googleusercontent.com">
 ```
 
 Read the rest of the instructions if you need to add extra APIs (like Google People API).
@@ -74,7 +72,21 @@ Find the example wiring in the [Google sign-in example application](https://gith
 
 See the [google_sign_in.dart](https://github.com/flutter/plugins/blob/master/packages/google_sign_in/google_sign_in/lib/google_sign_in.dart) for more API details.
 
+## Contributions and Testing
+
+Tests are a crucial to contributions to this package. All new contributions should be reasonably tested.
+
+In order to run tests in this package, do:
+
+```
+flutter test --platform chrome -j1
+```
+
+Contributions to this package are welcome. Read the [Contributing to Flutter Plugins](https://github.com/flutter/plugins/blob/master/CONTRIBUTING.md) guide to get started.
+
 ## Issues and feedback
 
 Please file [issues](https://github.com/flutter/flutter/issues/new)
-to send feedback or report a bug. Thank you!
+to send feedback or report a bug.
+
+**Thank you!**
diff --git a/packages/google_sign_in/google_sign_in_web/lib/google_sign_in_web.dart b/packages/google_sign_in/google_sign_in_web/lib/google_sign_in_web.dart
index 913cd25e6a85..4004d47d5551 100644
--- a/packages/google_sign_in/google_sign_in_web/lib/google_sign_in_web.dart
+++ b/packages/google_sign_in/google_sign_in_web/lib/google_sign_in_web.dart
@@ -5,14 +5,13 @@
 import 'dart:async';
 import 'dart:html' as html;
 
+import 'package:flutter/services.dart';
 import 'package:google_sign_in_platform_interface/google_sign_in_platform_interface.dart';
 import 'package:flutter_web_plugins/flutter_web_plugins.dart';
 import 'package:js/js.dart';
 import 'package:meta/meta.dart';
 
 import 'src/generated/gapiauth2.dart' as auth2;
-// TODO: Remove once this lands https://github.com/dart-lang/language/issues/671
-import 'src/generated/gapiauth2.dart' show GoogleAuthExtensions;
 import 'src/load_gapi.dart' as gapi;
 import 'src/utils.dart' show gapiUserToPluginUserData;
 
@@ -39,14 +38,27 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
   }
 
   Future<void> _isGapiInitialized;
+  Future<void> _isAuthInitialized;
+  bool _isInitCalled = false;
+
+  // This method throws if init hasn't been called at some point in the past.
+  // It is used by the [initialized] getter to ensure that users can't await
+  // on a Future that will never resolve.
+  void _assertIsInitCalled() {
+    if (!_isInitCalled) {
+      throw StateError(
+          'GoogleSignInPlugin::init() must be called before any other method in this plugin.');
+    }
+  }
 
-  /// This is only exposed for testing. It shouldn't be accessed by users of the
-  /// plugin as it could break at any point.
+  /// A future that resolves when both GAPI and Auth2 have been correctly initialized.
   @visibleForTesting
-  Future<void> get initialized => _isGapiInitialized;
+  Future<void> get initialized {
+    _assertIsInitCalled();
+    return Future.wait([_isGapiInitialized, _isAuthInitialized]);
+  }
 
   String _autoDetectedClientId;
-  FutureOr<auth2.GoogleUser> _lastSeenUser;
 
   /// Factory method that initializes the plugin with [GoogleSignInPlatform].
   static void registerWith(Registrar registrar) {
@@ -72,7 +84,7 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
         'Check https://developers.google.com/identity/protocols/googlescopes '
         'for a list of valid OAuth 2.0 scopes.');
 
-    await initialized;
+    await _isGapiInitialized;
 
     final auth2.GoogleAuth auth = auth2.init(auth2.ClientConfig(
       hosted_domain: hostedDomain,
@@ -81,19 +93,26 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
       client_id: appClientId,
     ));
 
-    // Subscribe to changes in the auth instance returned by init,
-    // and cache the _lastSeenUser as we get notified of new values.
-    final Completer<auth2.GoogleUser> initUserCompleter =
-        Completer<auth2.GoogleUser>();
-
-    auth.currentUser.listen(allowInterop((auth2.GoogleUser nextUser) {
-      if (!initUserCompleter.isCompleted) {
-        initUserCompleter.complete(nextUser);
-      } else {
-        _lastSeenUser = nextUser;
-      }
+    Completer<void> isAuthInitialized = Completer<void>();
+    _isAuthInitialized = isAuthInitialized.future;
+    _isInitCalled = true;
+
+    auth.then(allowInterop((auth2.GoogleAuth initializedAuth) {
+      // onSuccess
+
+      // TODO: https://github.com/flutter/flutter/issues/48528
+      // This plugin doesn't notify the app of external changes to the
+      // state of the authentication, i.e: if you logout elsewhere...
+
+      isAuthInitialized.complete();
+    }), allowInterop((dynamic reason) {
+      // onError
+      throw PlatformException(
+        code: 'google_sign_in',
+        message: reason.error,
+        details: reason.details,
+      );
     }));
-    _lastSeenUser = initUserCompleter.future;
 
     return null;
   }
@@ -102,7 +121,8 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
   Future<GoogleSignInUserData> signInSilently() async {
     await initialized;
 
-    return gapiUserToPluginUserData(await _lastSeenUser);
+    return gapiUserToPluginUserData(
+        await auth2.getAuthInstance().currentUser.get());
   }
 
   @override
@@ -154,7 +174,6 @@ class GoogleSignInPlugin extends GoogleSignInPlatform {
   Future<void> clearAuthCache({String token}) async {
     await initialized;
 
-    _lastSeenUser = null;
     return auth2.getAuthInstance().disconnect();
   }
 }
diff --git a/packages/google_sign_in/google_sign_in_web/pubspec.yaml b/packages/google_sign_in/google_sign_in_web/pubspec.yaml
index 2790ef8d4b59..a19453ad8ba7 100644
--- a/packages/google_sign_in/google_sign_in_web/pubspec.yaml
+++ b/packages/google_sign_in/google_sign_in_web/pubspec.yaml
@@ -2,7 +2,7 @@ name: google_sign_in_web
 description: Flutter plugin for Google Sign-In, a secure authentication system
   for signing in with a Google account on Android, iOS and Web.
 homepage: https://github.com/flutter/plugins/tree/master/packages/google_sign_in/google_sign_in_web
-version: 0.8.2+1
+version: 0.8.3
 
 flutter:
   plugin:
diff --git a/packages/google_sign_in/google_sign_in_web/test/auth2_test.dart b/packages/google_sign_in/google_sign_in_web/test/auth2_test.dart
index 6eae93a136c8..7a3a01227169 100644
--- a/packages/google_sign_in/google_sign_in_web/test/auth2_test.dart
+++ b/packages/google_sign_in/google_sign_in_web/test/auth2_test.dart
@@ -27,9 +27,8 @@ void main() {
 
   GoogleSignInPlugin plugin;
 
-  setUp(() async {
+  setUp(() {
     plugin = GoogleSignInPlugin();
-    await plugin.initialized;
   });
 
   test('Init requires clientId', () async {
@@ -47,12 +46,13 @@ void main() {
   });
 
   group('Successful .init, then', () {
-    setUp(() {
-      plugin.init(
+    setUp(() async {
+      await plugin.init(
         hostedDomain: 'foo',
         scopes: <String>['some', 'scope'],
         clientId: '1234',
       );
+      await plugin.initialized;
     });
 
     test('signInSilently', () async {
diff --git a/packages/google_sign_in/google_sign_in_web/test/gapi_load_test.dart b/packages/google_sign_in/google_sign_in_web/test/gapi_load_test.dart
index 815dcdcfc645..6703beca2cad 100644
--- a/packages/google_sign_in/google_sign_in_web/test/gapi_load_test.dart
+++ b/packages/google_sign_in/google_sign_in_web/test/gapi_load_test.dart
@@ -7,14 +7,16 @@
 import 'dart:html' as html;
 
 import 'package:flutter_test/flutter_test.dart';
+import 'package:google_sign_in_platform_interface/google_sign_in_platform_interface.dart';
 import 'package:google_sign_in_web/google_sign_in_web.dart';
 import 'gapi_mocks/gapi_mocks.dart' as gapi_mocks;
 import 'utils.dart';
 
 void main() {
-  gapiUrl = toBase64Url(gapi_mocks.gapiInitSuccess());
+  gapiUrl = toBase64Url(gapi_mocks.auth2InitSuccess(GoogleSignInUserData()));
 
-  test('Plugin is initialized after GAPI fully loads', () async {
+  test('Plugin is initialized after GAPI fully loads and init is called',
+      () async {
     expect(
       html.querySelector('script[src^="data:"]'),
       isNull,
@@ -26,6 +28,12 @@ void main() {
       isNotNull,
       reason: 'Mock script should be injected',
     );
+    expect(() {
+      plugin.initialized;
+    }, throwsStateError,
+        reason:
+            'The plugin should throw if checking for `initialized` before calling .init');
+    await plugin.init(hostedDomain: '', clientId: '');
     await plugin.initialized;
     expect(
       plugin.initialized,
diff --git a/packages/google_sign_in/google_sign_in_web/test/gapi_mocks/gapi_mocks.dart b/packages/google_sign_in/google_sign_in_web/test/gapi_mocks/gapi_mocks.dart
index d36cd5edf63a..9a7d4f403f97 100644
--- a/packages/google_sign_in/google_sign_in_web/test/gapi_mocks/gapi_mocks.dart
+++ b/packages/google_sign_in/google_sign_in_web/test/gapi_mocks/gapi_mocks.dart
@@ -10,5 +10,4 @@ import 'src/gapi.dart';
 import 'src/google_user.dart';
 import 'src/test_iife.dart';
 
-part 'src/gapi_load.dart';
 part 'src/auth2_init.dart';
diff --git a/packages/google_sign_in/google_sign_in_web/test/gapi_mocks/src/auth2_init.dart b/packages/google_sign_in/google_sign_in_web/test/gapi_mocks/src/auth2_init.dart
index 5484dc5b61bc..1846033151c1 100644
--- a/packages/google_sign_in/google_sign_in_web/test/gapi_mocks/src/auth2_init.dart
+++ b/packages/google_sign_in/google_sign_in_web/test/gapi_mocks/src/auth2_init.dart
@@ -13,6 +13,11 @@ var mockUser = ${googleUser(userData)};
 function GapiAuth2() {}
 GapiAuth2.prototype.init = function (initOptions) {
   return {
+    then: (onSuccess, onError) => {
+      window.setTimeout(() => {
+        onSuccess(window.gapi.auth2);
+      }, 30);
+    },
     currentUser: {
       listen: (cb) => {
         window.setTimeout(() => {
diff --git a/packages/google_sign_in/google_sign_in_web/test/gapi_mocks/src/gapi_load.dart b/packages/google_sign_in/google_sign_in_web/test/gapi_mocks/src/gapi_load.dart
deleted file mode 100644
index f390500f6f4e..000000000000
--- a/packages/google_sign_in/google_sign_in_web/test/gapi_mocks/src/gapi_load.dart
+++ /dev/null
@@ -1,8 +0,0 @@
-// Copyright 2019 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-part of gapi_mocks;
-
-// JS mock of a raw GAPI object.
-String gapiInitSuccess() => testIife(gapi());