diff --git a/packages/auth/src/OAuth/GenericOAuthClient.php b/packages/auth/src/OAuth/GenericOAuthClient.php
index 9b591f26ee..2f1bd8db42 100644
--- a/packages/auth/src/OAuth/GenericOAuthClient.php
+++ b/packages/auth/src/OAuth/GenericOAuthClient.php
@@ -120,7 +120,7 @@ public function authenticate(Request $request, Closure $map): Authenticatable
 
         $this->session->remove($this->sessionKey);
 
-        if ($expectedState !== $actualState) {
+        if ($expectedState === null || $expectedState === '' || $expectedState !== $actualState) {
             throw new OAuthStateWasInvalid();
         }
 
diff --git a/packages/auth/src/OAuth/Testing/TestingOAuthClient.php b/packages/auth/src/OAuth/Testing/TestingOAuthClient.php
index 470cf0ccd7..f38a654056 100644
--- a/packages/auth/src/OAuth/Testing/TestingOAuthClient.php
+++ b/packages/auth/src/OAuth/Testing/TestingOAuthClient.php
@@ -130,7 +130,7 @@ public function authenticate(Request $request, Closure $map): Authenticatable
 
         $this->state = null;
 
-        if ($expectedState !== $actualState) {
+        if ($expectedState === null || $expectedState === '' || $expectedState !== $actualState) {
             throw new OAuthStateWasInvalid();
         }
 
diff --git a/tests/Integration/Auth/OAuth/GenericOAuthClientTest.php b/tests/Integration/Auth/OAuth/GenericOAuthClientTest.php
index c1ad063c9e..f5fc9cf162 100644
--- a/tests/Integration/Auth/OAuth/GenericOAuthClientTest.php
+++ b/tests/Integration/Auth/OAuth/GenericOAuthClientTest.php
@@ -2,12 +2,22 @@
 
 namespace Tests\Tempest\Integration\Auth\OAuth;
 
+use League\OAuth2\Client\Provider\AbstractProvider;
+use League\OAuth2\Client\Provider\ResourceOwnerInterface;
+use League\OAuth2\Client\Token\AccessToken;
+use LogicException;
 use PHPUnit\Framework\Attributes\Test;
+use Psr\Http\Message\ResponseInterface;
+use ReflectionClass;
+use Tempest\Auth\Exceptions\OAuthStateWasInvalid;
 use Tempest\Auth\Exceptions\OAuthWasNotConfigured;
 use Tempest\Auth\OAuth\Config\GitHubOAuthConfig;
 use Tempest\Auth\OAuth\GenericOAuthClient;
 use Tempest\Auth\OAuth\OAuthClient;
+use Tempest\Http\GenericRequest;
+use Tempest\Http\Method;
 use Tempest\Http\Session\Session;
+use Tempest\Support\Uri;
 use Tests\Tempest\Integration\FrameworkIntegrationTestCase;
 
 final class GenericOAuthClientTest extends FrameworkIntegrationTestCase
@@ -52,4 +62,63 @@ public function state_is_set_when_redirect_is_created(): void
 
         $this->assertNotNull($session->get($oauth->sessionKey));
     }
+
+    #[Test]
+    public function missing_session_state_is_rejected(): void
+    {
+        $this->container->config(new GitHubOAuthConfig(
+            clientId: 'client-id',
+            clientSecret: 'client-secret', // @mago-expect lint:no-literal-password
+            redirectTo: '/oauth/callback',
+            scopes: ['user:email'],
+        ));
+
+        /** @var GenericOAuthClient $oauth */
+        $oauth = $this->container->get(OAuthClient::class);
+
+        $reflection = new ReflectionClass($oauth);
+        $reflection->getProperty('provider')->setValue($oauth, new class extends AbstractProvider {
+            public function getBaseAuthorizationUrl(): string
+            {
+                return 'https://provider.test/authorize';
+            }
+
+            public function getBaseAccessTokenUrl(array $params): string
+            {
+                return 'https://provider.test/token';
+            }
+
+            public function getResourceOwnerDetailsUrl(AccessToken $token): string
+            {
+                return 'https://provider.test/user';
+            }
+
+            public function getAccessToken($grant, array $options = [])
+            {
+                throw new LogicException('Access token should not be requested when state is missing.');
+            }
+
+            protected function getDefaultScopes(): array
+            {
+                return [];
+            }
+
+            protected function checkResponse(ResponseInterface $response, $data): void {}
+
+            protected function createResourceOwner(array $response, AccessToken $token): ResourceOwnerInterface
+            {
+                throw new LogicException('Resource owner should not be created when state is missing.');
+            }
+        });
+
+        $this->expectException(OAuthStateWasInvalid::class);
+
+        $oauth->authenticate(
+            request: new GenericRequest(
+                method: Method::GET,
+                uri: Uri\set_query('/oauth/callback', code: 'auth-code'),
+            ),
+            map: static fn () => throw new LogicException('User should not be mapped when state is missing.'),
+        );
+    }
 }
diff --git a/tests/Integration/Auth/OAuth/TestingOAuthClientTest.php b/tests/Integration/Auth/OAuth/TestingOAuthClientTest.php
index 87279d839b..c11867d825 100644
--- a/tests/Integration/Auth/OAuth/TestingOAuthClientTest.php
+++ b/tests/Integration/Auth/OAuth/TestingOAuthClientTest.php
@@ -327,6 +327,34 @@ public function state_is_cleared_even_when_validation_fails(): void
 
         $this->assertNull($client->getState());
     }
+
+    #[Test]
+    public function missing_state_is_rejected(): void
+    {
+        $this->database->reset(migrate: false);
+        $this->database->migrate(CreateMigrationsTable::class, CreateUsersTable::class);
+
+        $this->container->config(new GitHubOAuthConfig(
+            clientId: 'foo',
+            clientSecret: 'bar', // @mago-expect lint:no-literal-password
+            redirectTo: '/oauth/github',
+        ));
+
+        $client = $this->oauth->fake($this->user);
+
+        $this->expectException(OAuthStateWasInvalid::class);
+
+        $client->authenticate(
+            request: new GenericRequest(
+                method: Method::GET,
+                uri: Uri\set_query('/oauth/callback', code: 'auth-code'),
+            ),
+            map: static fn (OAuthUser $user): User => query(User::class)->updateOrCreate(
+                ['github_id' => $user->id],
+                ['email' => $user->email ?? '', 'full_name' => $user->name ?? '', 'username' => $user->nickname ?? ''],
+            ),
+        );
+    }
 }
 
 final class User implements Authenticatable