diff --git a/src/bundle/DependencyInjection/Factory/Security/TwoFactorFactory.php b/src/bundle/DependencyInjection/Factory/Security/TwoFactorFactory.php
index 62d229b4..8ec3c7e0 100644
--- a/src/bundle/DependencyInjection/Factory/Security/TwoFactorFactory.php
+++ b/src/bundle/DependencyInjection/Factory/Security/TwoFactorFactory.php
@@ -136,7 +136,8 @@ private function createAuthenticatorService(
             ->replaceArgument(0, new Reference($twoFactorFirewallConfigId))
             ->replaceArgument(2, new Reference($successHandlerId))
             ->replaceArgument(3, new Reference($failureHandlerId))
-            ->replaceArgument(4, new Reference($authRequiredHandlerId));
+            ->replaceArgument(4, new Reference($authRequiredHandlerId))
+            ->addTag('kernel.reset', ['method' => 'reset']);
 
         return $authenticatorId;
     }
diff --git a/src/bundle/DependencyInjection/Factory/Security/TwoFactorServicesFactory.php b/src/bundle/DependencyInjection/Factory/Security/TwoFactorServicesFactory.php
index 9344f306..bedf61c2 100644
--- a/src/bundle/DependencyInjection/Factory/Security/TwoFactorServicesFactory.php
+++ b/src/bundle/DependencyInjection/Factory/Security/TwoFactorServicesFactory.php
@@ -107,7 +107,8 @@ public function createProviderPreparationListener(ContainerBuilder $container, s
             ->replaceArgument(3, $firewallName)
             ->replaceArgument(4, $config['prepare_on_login'] ?? TwoFactorFactory::DEFAULT_PREPARE_ON_LOGIN)
             ->replaceArgument(5, $config['prepare_on_access_denied'] ?? TwoFactorFactory::DEFAULT_PREPARE_ON_ACCESS_DENIED)
-            ->addTag('kernel.event_subscriber');
+            ->addTag('kernel.event_subscriber')
+            ->addTag('kernel.reset', ['method' => 'reset']);
     }
 
     public function createKernelExceptionListener(ContainerBuilder $container, string $firewallName, string $authRequiredHandlerId): void
diff --git a/src/bundle/Resources/config/security.php b/src/bundle/Resources/config/security.php
index 4728c36a..d5a25d54 100644
--- a/src/bundle/Resources/config/security.php
+++ b/src/bundle/Resources/config/security.php
@@ -30,6 +30,7 @@
     $container->services()
         ->set('scheb_two_factor.security.authenticator', TwoFactorAuthenticator::class)
             ->tag('monolog.logger', ['channel' => 'security'])
+            ->tag('kernel.reset', ['method' => 'reset'])
             ->args([
                 abstract_arg('Two-factor firewall config'),
                 service('security.token_storage'),
diff --git a/tests/DependencyInjection/ResettableServicesAreTaggedTest.php b/tests/DependencyInjection/ResettableServicesAreTaggedTest.php
new file mode 100644
index 00000000..8520f8cf
--- /dev/null
+++ b/tests/DependencyInjection/ResettableServicesAreTaggedTest.php
@@ -0,0 +1,120 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Scheb\TwoFactorBundle\Tests\DependencyInjection;
+
+use PHPUnit\Framework\Attributes\Test;
+use ReflectionClass;
+use Scheb\TwoFactorBundle\DependencyInjection\Factory\Security\TwoFactorFactory;
+use Scheb\TwoFactorBundle\DependencyInjection\Factory\Security\TwoFactorServicesFactory;
+use Scheb\TwoFactorBundle\DependencyInjection\SchebTwoFactorExtension;
+use Scheb\TwoFactorBundle\Tests\TestCase;
+use Symfony\Component\DependencyInjection\Compiler\ResolveChildDefinitionsPass;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Definition;
+use Symfony\Contracts\Service\ResetInterface;
+use function class_exists;
+use function implode;
+use function sprintf;
+
+/**
+ * A service implementing {@see ResetInterface} is only reset when it carries the `kernel.reset` tag.
+ *
+ * The per-firewall services are `ChildDefinition`s, and a child does NOT inherit its parent's tags,
+ * so tagging the abstract parent in `security.php` is not enough: the tag has to be re-added to each
+ * child. Nothing fails at compile time when it is missing, and under PHP-FPM nothing fails at
+ * runtime either, because every request builds a new container. The state only survives into the
+ * next request under a persistent worker (FrankenPHP, RoadRunner, Swoole).
+ *
+ * This asserts the property rather than a list of known service ids: it resolves the child
+ * definitions, then requires the tag of EVERY resolved definition whose class implements
+ * `ResetInterface`. A future resettable service added without the tag fails here without anyone
+ * having to remember to extend the test.
+ */
+class ResettableServicesAreTaggedTest extends TestCase
+{
+    private const string FIREWALL_NAME = 'firewallName';
+    private const string USER_PROVIDER = 'userProvider';
+    private const string RESET_TAG = 'kernel.reset';
+
+    #[Test]
+    public function createAuthenticator_resettableServiceDefinitions_allCarryTheResetTag(): void
+    {
+        $container = $this->compileContainerWithTwoFactorFirewall();
+
+        $untagged = [];
+        foreach ($container->getDefinitions() as $id => $definition) {
+            if (!$this->isResettable($definition)) {
+                continue;
+            }
+
+            if ($definition->hasTag(self::RESET_TAG)) {
+                continue;
+            }
+
+            $untagged[] = $id;
+        }
+
+        $this->assertSame([], $untagged, sprintf(
+            'These services implement %s but carry no "%s" tag, so their state survives into the next request under a persistent worker: %s',
+            ResetInterface::class,
+            self::RESET_TAG,
+            implode(', ', $untagged),
+        ));
+    }
+
+    /**
+     * The control for the arm above: without at least one resettable definition to look at, an empty
+     * `$untagged` would pass against any container at all.
+     */
+    #[Test]
+    public function createAuthenticator_resettableServiceDefinitions_areActuallyPresent(): void
+    {
+        $container = $this->compileContainerWithTwoFactorFirewall();
+
+        $resettable = [];
+        foreach ($container->getDefinitions() as $id => $definition) {
+            if (!$this->isResettable($definition)) {
+                continue;
+            }
+
+            $resettable[] = $id;
+        }
+
+        $this->assertNotEmpty($resettable, 'No resettable service was found, so the assertion above examined nothing');
+    }
+
+    private function isResettable(Definition $definition): bool
+    {
+        $class = $definition->getClass();
+
+        if (null === $class || !class_exists($class)) {
+            return false;
+        }
+
+        return (new ReflectionClass($class))->implementsInterface(ResetInterface::class);
+    }
+
+    private function compileContainerWithTwoFactorFirewall(): ContainerBuilder
+    {
+        $container = new ContainerBuilder();
+
+        // Stub services the extension's configuration refers to.
+        $container->setDefinition('acme_test.persister', new Definition());
+        $container->setDefinition('acme_test.mailer', new Definition());
+
+        $extension = new SchebTwoFactorExtension();
+        $extension->load([[]], $container);
+
+        $factory = new TwoFactorFactory(new TwoFactorServicesFactory());
+        $factory->createAuthenticator($container, self::FIREWALL_NAME, [], self::USER_PROVIDER);
+        $factory->createListeners($container, self::FIREWALL_NAME, []);
+
+        // Resolves every ChildDefinition against its parent, which is what gives the per-firewall
+        // definitions their class — and what drops any tag the child did not re-add.
+        (new ResolveChildDefinitionsPass())->process($container);
+
+        return $container;
+    }
+}