diff --git a/packages/google_sign_in/CHANGELOG.md b/packages/google_sign_in/CHANGELOG.md
index 0a4e8d21cca8..bbbba373b3d9 100644
--- a/packages/google_sign_in/CHANGELOG.md
+++ b/packages/google_sign_in/CHANGELOG.md
@@ -1,3 +1,8 @@
+## 4.0.3
+
+* Update guava to `27.0.1-android`.
+* Add correct @NonNull annotations to reduce compiler warnings.
+
 ## 4.0.2
 
 * Add missing template type parameter to `invokeMethod` calls.
diff --git a/packages/google_sign_in/android/build.gradle b/packages/google_sign_in/android/build.gradle
index 9162c3080e50..c6e0acdb5ff8 100755
--- a/packages/google_sign_in/android/build.gradle
+++ b/packages/google_sign_in/android/build.gradle
@@ -48,5 +48,5 @@ android {
 
 dependencies {
     api 'com.google.android.gms:play-services-auth:16.0.1'
-    implementation 'com.google.guava:guava:20.0'
+    implementation 'com.google.guava:guava:27.0.1-android'
 }
diff --git a/packages/google_sign_in/android/src/main/java/io/flutter/plugins/googlesignin/GoogleSignInPlugin.java b/packages/google_sign_in/android/src/main/java/io/flutter/plugins/googlesignin/GoogleSignInPlugin.java
index d2fc260c7b1c..5c292414057d 100755
--- a/packages/google_sign_in/android/src/main/java/io/flutter/plugins/googlesignin/GoogleSignInPlugin.java
+++ b/packages/google_sign_in/android/src/main/java/io/flutter/plugins/googlesignin/GoogleSignInPlugin.java
@@ -7,6 +7,8 @@
 import android.accounts.Account;
 import android.app.Activity;
 import android.content.Intent;
+import android.text.TextUtils;
+import androidx.annotation.NonNull;
 import com.google.android.gms.auth.GoogleAuthUtil;
 import com.google.android.gms.auth.UserRecoverableAuthException;
 import com.google.android.gms.auth.api.signin.GoogleSignIn;
@@ -20,8 +22,6 @@
 import com.google.android.gms.tasks.OnCompleteListener;
 import com.google.android.gms.tasks.RuntimeExecutionException;
 import com.google.android.gms.tasks.Task;
-import com.google.common.base.Joiner;
-import com.google.common.base.Strings;
 import io.flutter.plugin.common.MethodCall;
 import io.flutter.plugin.common.MethodChannel;
 import io.flutter.plugin.common.MethodChannel.MethodCallHandler;
@@ -107,7 +107,7 @@ public void onMethodCall(MethodCall call, Result result) {
 
   /**
    * A delegate interface that exposes all of the sign-in functionality for other plugins to use.
-   * The below {@link #Delegate} implementation should be used by any clients unless they need to
+   * The below {@link Delegate} implementation should be used by any clients unless they need to
    * override some of these functions, such as for testing.
    */
   public interface IDelegate {
@@ -243,7 +243,7 @@ public void init(
         for (String scope : requestedScopes) {
           optionsBuilder.requestScopes(new Scope(scope));
         }
-        if (!Strings.isNullOrEmpty(hostedDomain)) {
+        if (!TextUtils.isEmpty(hostedDomain)) {
           optionsBuilder.setHostedDomain(hostedDomain);
         }
 
@@ -270,7 +270,7 @@ public void signInSilently(Result result) {
         task.addOnCompleteListener(
             new OnCompleteListener<GoogleSignInAccount>() {
               @Override
-              public void onComplete(Task<GoogleSignInAccount> task) {
+              public void onComplete(@NonNull Task<GoogleSignInAccount> task) {
                 onSignInResult(task);
               }
             });
@@ -305,7 +305,7 @@ public void signOut(Result result) {
           .addOnCompleteListener(
               new OnCompleteListener<Void>() {
                 @Override
-                public void onComplete(Task<Void> task) {
+                public void onComplete(@NonNull Task<Void> task) {
                   if (task.isSuccessful()) {
                     finishWithSuccess(null);
                   } else {
@@ -325,7 +325,7 @@ public void disconnect(Result result) {
           .addOnCompleteListener(
               new OnCompleteListener<Void>() {
                 @Override
-                public void onComplete(Task<Void> task) {
+                public void onComplete(@NonNull Task<Void> task) {
                   if (task.isSuccessful()) {
                     finishWithSuccess(null);
                   } else {
@@ -448,7 +448,7 @@ public void getTokens(
             @Override
             public String call() throws Exception {
               Account account = new Account(email, "com.google");
-              String scopesStr = "oauth2:" + Joiner.on(' ').join(requestedScopes);
+              String scopesStr = "oauth2:" + TextUtils.join(" ", requestedScopes);
               return GoogleAuthUtil.getToken(registrar.context(), account, scopesStr);
             }
           };
diff --git a/packages/google_sign_in/pubspec.yaml b/packages/google_sign_in/pubspec.yaml
index 4a14005956ca..f9c18839b048 100755
--- a/packages/google_sign_in/pubspec.yaml
+++ b/packages/google_sign_in/pubspec.yaml
@@ -3,7 +3,7 @@ description: Flutter plugin for Google Sign-In, a secure authentication system
   for signing in with a Google account on Android and iOS.
 author: Flutter Team <flutter-dev@googlegroups.com>
 homepage: https://github.com/flutter/plugins/tree/master/packages/google_sign_in
-version: 4.0.2
+version: 4.0.3
 
 flutter:
   plugin: