diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 1a433c2..885423e 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -130,6 +130,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Fixed
+
+- **`locale.unlocalized: serve`:** `UnlocalizedDefaultLocaleSubscriber` forces `locale.default` at request time on AuthKit `*_unlocalized` routes (after Symfony `LocaleListener`), so bare `/login` (etc.) stays correct when the compiled route `_locale` default was warmed with a different value (Docker image build vs runtime env).
+
 ## [1.22.0] - 2026-09-28
 
 ### Security
diff --git a/docs/CONFIGURATION.md b/docs/CONFIGURATION.md
index 46c5e8e..4fa818d 100644
--- a/docs/CONFIGURATION.md
+++ b/docs/CONFIGURATION.md
@@ -465,7 +465,7 @@ nowo_auth_kit:
 When `in_path: both`:
 
 - `unlocalized: redirect` — bare URL redirects to `/{default}/…` (or current request locale via `auth_kit_route_params()`).
-- `unlocalized: serve` — bare URL renders with `_locale = locale.default`.
+- `unlocalized: serve` — bare URL renders with `_locale = locale.default`. `UnlocalizedDefaultLocaleSubscriber` (priority `14`) re-applies `locale.default` on each request so a stale warmed route cache cannot stick a wrong locale on `/login` (image build vs runtime `DEFAULT_LOCALE`).
 
 Legacy keys `default_locale`, `enabled_locales`, and `locale_in_path` (bool) still work and map into `locale.*`.
 
diff --git a/specs/001-baseline/code-inventory.md b/specs/001-baseline/code-inventory.md
index 24a205f..99fd27d 100644
--- a/specs/001-baseline/code-inventory.md
+++ b/specs/001-baseline/code-inventory.md
@@ -34,6 +34,7 @@ Every production file under `src/` is listed exactly once. Status **Mapped** mea
 | `DeviceIntelligence/NewDeviceLoginNotifierInterface.php` | production | FR-DIINTEL-001 | Mapped |
 | `DeviceIntelligence/NullNewDeviceLoginNotifier.php` | production | FR-DIINTEL-001 | Mapped |
 | `EventSubscriber/NewDeviceLoginSubscriber.php` | production | FR-DIINTEL-001 | Mapped |
+| `EventSubscriber/UnlocalizedDefaultLocaleSubscriber.php` | production | FR-LOCALE-001 | Mapped |
 
 ## HTTP controllers
 
diff --git a/specs/001-baseline/spec.md b/specs/001-baseline/spec.md
index ef059da..d74c8e7 100644
--- a/specs/001-baseline/spec.md
+++ b/specs/001-baseline/spec.md
@@ -107,7 +107,7 @@ Drop-in Symfony **authentication kit**: login/logout, gated registration, rememb
 ### Profiles & locale
 
 - **FR-PROFILE-001**: `ProfileSettings`, `ProfileRegistry`, `RequestProfileResolver`, `UnknownProfileException`.
-- **FR-LOCALE-001**: Locale-in-path / unlocalized redirect modes and `UnlocalizedLocaleRedirectController`.
+- **FR-LOCALE-001**: Locale-in-path / unlocalized redirect modes and `UnlocalizedLocaleRedirectController`. When `unlocalized: serve`, `UnlocalizedDefaultLocaleSubscriber` forces `locale.default` at runtime on `*_unlocalized` AuthKit routes (covers warmed route-cache vs runtime env drift).
 
 ### Security integration
 
diff --git a/src/EventSubscriber/UnlocalizedDefaultLocaleSubscriber.php b/src/EventSubscriber/UnlocalizedDefaultLocaleSubscriber.php
new file mode 100644
index 0000000..a09c91a
--- /dev/null
+++ b/src/EventSubscriber/UnlocalizedDefaultLocaleSubscriber.php
@@ -0,0 +1,72 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Nowo\AuthKitBundle\EventSubscriber;
+
+use Nowo\AuthKitBundle\Enum\UnlocalizedLocaleMode;
+use Nowo\AuthKitBundle\Profile\RequestProfileResolver;
+use Nowo\AuthKitBundle\Routing\AuthKitRouteLoader;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+use Symfony\Component\HttpKernel\Event\RequestEvent;
+use Symfony\Component\HttpKernel\KernelEvents;
+use Symfony\Contracts\Translation\LocaleAwareInterface;
+use Symfony\Contracts\Translation\TranslatorInterface;
+
+use function is_string;
+use function str_ends_with;
+use function strtolower;
+
+/**
+ * Forces {@code locale.default} on AuthKit {@code *_unlocalized} twins when {@code unlocalized: serve}.
+ *
+ * Bare {@code /login} (etc.) must render the configured default even when the compiled route
+ * {@code _locale} default was warmed with a different value (image build vs runtime env).
+ */
+final readonly class UnlocalizedDefaultLocaleSubscriber implements EventSubscriberInterface
+{
+    private UnlocalizedLocaleMode $unlocalizedMode;
+
+    public function __construct(
+        private TranslatorInterface $translator,
+        private string $defaultLocale,
+        string $unlocalizedMode = 'redirect',
+    ) {
+        $this->unlocalizedMode = UnlocalizedLocaleMode::from($unlocalizedMode);
+    }
+
+    /**
+     * @return array<string, list<array{0: string, 1: int}>>
+     */
+    public static function getSubscribedEvents(): array
+    {
+        return [
+            // After LocaleListener (16) / LocaleAwareListener (15); before typical host sticky-session listeners.
+            KernelEvents::REQUEST => [['onKernelRequest', 14]],
+        ];
+    }
+
+    public function onKernelRequest(RequestEvent $event): void
+    {
+        if (!$event->isMainRequest() || $this->unlocalizedMode !== UnlocalizedLocaleMode::Serve) {
+            return;
+        }
+
+        $request = $event->getRequest();
+        if (!$request->attributes->has(RequestProfileResolver::REQUEST_ATTRIBUTE)) {
+            return;
+        }
+
+        $route = $request->attributes->get('_route');
+        if (!is_string($route) || !str_ends_with($route, AuthKitRouteLoader::UNLOCALIZED_ROUTE_SUFFIX)) {
+            return;
+        }
+
+        $locale = strtolower($this->defaultLocale);
+        $request->attributes->set('_locale', $locale);
+        $request->setLocale($locale);
+        if ($this->translator instanceof LocaleAwareInterface) {
+            $this->translator->setLocale($locale);
+        }
+    }
+}
diff --git a/src/Resources/config/services.yaml b/src/Resources/config/services.yaml
index 21ad3b8..b4ac282 100644
--- a/src/Resources/config/services.yaml
+++ b/src/Resources/config/services.yaml
@@ -59,6 +59,11 @@ services:
             $defaultLocale: '%nowo_auth_kit.locale.default%'
             $enabledLocales: '%nowo_auth_kit.locale.enabled%'
 
+    Nowo\AuthKitBundle\EventSubscriber\UnlocalizedDefaultLocaleSubscriber:
+        arguments:
+            $defaultLocale: '%nowo_auth_kit.locale.default%'
+            $unlocalizedMode: '%nowo_auth_kit.locale.unlocalized%'
+
     Nowo\AuthKitBundle\Routing\AuthKitRouteLoader:
         arguments:
             $profiles: '%nowo_auth_kit.profiles%'
diff --git a/tests/Unit/EventSubscriber/UnlocalizedDefaultLocaleSubscriberTest.php b/tests/Unit/EventSubscriber/UnlocalizedDefaultLocaleSubscriberTest.php
new file mode 100644
index 0000000..a85963a
--- /dev/null
+++ b/tests/Unit/EventSubscriber/UnlocalizedDefaultLocaleSubscriberTest.php
@@ -0,0 +1,129 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Nowo\AuthKitBundle\Tests\Unit\EventSubscriber;
+
+use Nowo\AuthKitBundle\EventSubscriber\UnlocalizedDefaultLocaleSubscriber;
+use Nowo\AuthKitBundle\Profile\RequestProfileResolver;
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\HttpFoundation\Request;
+use Symfony\Component\HttpKernel\Event\RequestEvent;
+use Symfony\Component\HttpKernel\HttpKernelInterface;
+use Symfony\Component\HttpKernel\KernelEvents;
+use Symfony\Component\HttpKernel\KernelInterface;
+use Symfony\Contracts\Translation\LocaleAwareInterface;
+use Symfony\Contracts\Translation\TranslatorInterface;
+
+final class UnlocalizedDefaultLocaleSubscriberTest extends TestCase
+{
+    public function testSubscribesAfterLocaleAwareListener(): void
+    {
+        self::assertSame(
+            [KernelEvents::REQUEST => [['onKernelRequest', 14]]],
+            UnlocalizedDefaultLocaleSubscriber::getSubscribedEvents(),
+        );
+    }
+
+    public function testForcesDefaultLocaleOnUnlocalizedAuthRouteWhenServe(): void
+    {
+        $translator = new RecordingTranslator();
+        $request    = Request::create('/login');
+        $request->attributes->set('_route', 'nowo_auth_kit_login_unlocalized');
+        $request->attributes->set(RequestProfileResolver::REQUEST_ATTRIBUTE, 'default');
+        $request->attributes->set('_locale', 'en');
+        $request->setLocale('en');
+        $event = $this->mainEvent($request);
+
+        new UnlocalizedDefaultLocaleSubscriber($translator, 'es', 'serve')->onKernelRequest($event);
+
+        self::assertSame('es', $request->getLocale());
+        self::assertSame('es', $request->attributes->get('_locale'));
+        self::assertSame('es', $translator->locale);
+    }
+
+    public function testIgnoresWhenUnlocalizedModeIsRedirect(): void
+    {
+        $translator = new RecordingTranslator();
+        $request    = Request::create('/login');
+        $request->attributes->set('_route', 'nowo_auth_kit_login_unlocalized');
+        $request->attributes->set(RequestProfileResolver::REQUEST_ATTRIBUTE, 'default');
+        $request->attributes->set('_locale', 'en');
+        $request->setLocale('en');
+        $event = $this->mainEvent($request);
+
+        new UnlocalizedDefaultLocaleSubscriber($translator, 'es', 'redirect')->onKernelRequest($event);
+
+        self::assertSame('en', $request->getLocale());
+        self::assertSame('en', $request->attributes->get('_locale'));
+        self::assertSame('en', $translator->locale);
+    }
+
+    public function testIgnoresLocalizedAuthRoutes(): void
+    {
+        $translator = new RecordingTranslator();
+        $request    = Request::create('/en/login');
+        $request->attributes->set('_route', 'nowo_auth_kit_login');
+        $request->attributes->set(RequestProfileResolver::REQUEST_ATTRIBUTE, 'default');
+        $request->attributes->set('_locale', 'en');
+        $request->setLocale('en');
+        $event = $this->mainEvent($request);
+
+        new UnlocalizedDefaultLocaleSubscriber($translator, 'es', 'serve')->onKernelRequest($event);
+
+        self::assertSame('en', $request->getLocale());
+        self::assertSame('en', $request->attributes->get('_locale'));
+        self::assertSame('en', $translator->locale);
+    }
+
+    public function testIgnoresNonAuthKitUnlocalizedRoutes(): void
+    {
+        $translator = new RecordingTranslator();
+        $request    = Request::create('/setup');
+        $request->attributes->set('_route', 'nowo_site_backup_setup_unlocalized');
+        $request->attributes->set('_locale', 'en');
+        $request->setLocale('en');
+        $event = $this->mainEvent($request);
+
+        new UnlocalizedDefaultLocaleSubscriber($translator, 'es', 'serve')->onKernelRequest($event);
+
+        self::assertSame('en', $request->getLocale());
+        self::assertSame('en', $request->attributes->get('_locale'));
+        self::assertSame('en', $translator->locale);
+    }
+
+    private function mainEvent(Request $request): RequestEvent
+    {
+        return new RequestEvent(
+            $this->createStub(KernelInterface::class),
+            $request,
+            HttpKernelInterface::MAIN_REQUEST,
+        );
+    }
+}
+
+/**
+ * @internal
+ */
+final class RecordingTranslator implements TranslatorInterface, LocaleAwareInterface
+{
+    public string $locale = 'en';
+
+    /**
+     * @param array<string, mixed> $parameters
+     */
+    public function trans(string $id, array $parameters = [], ?string $domain = null, ?string $locale = null): string
+    {
+        return $id;
+    }
+
+    public function getLocale(): string
+    {
+        return $this->locale;
+    }
+
+    public function setLocale(string $locale): void
+    {
+        $this->locale = $locale;
+    }
+}