diff --git a/src/Auth/Eloquent/User.php b/src/Auth/Eloquent/User.php
index 35094be0bd6..f86ae94cef9 100644
--- a/src/Auth/Eloquent/User.php
+++ b/src/Auth/Eloquent/User.php
@@ -2,6 +2,7 @@
 
 namespace Statamic\Auth\Eloquent;
 
+use Carbon\CarbonInterface;
 use Illuminate\Database\Eloquent\Model;
 use Illuminate\Support\Carbon;
 use Illuminate\Support\Collection;
@@ -370,7 +371,7 @@ public function lastLogin()
             return null;
         }
 
-        return $date instanceof Carbon ? $date : Carbon::createFromFormat($this->model()->getDateFormat(), $date);
+        return $date instanceof CarbonInterface ? $date : Carbon::createFromFormat($this->model()->getDateFormat(), $date);
     }
 
     public function setLastLogin($time)
diff --git a/src/Auth/WebAuthn/Passkey.php b/src/Auth/WebAuthn/Passkey.php
index a807b4dded4..da354673b67 100644
--- a/src/Auth/WebAuthn/Passkey.php
+++ b/src/Auth/WebAuthn/Passkey.php
@@ -3,6 +3,7 @@
 namespace Statamic\Auth\WebAuthn;
 
 use Carbon\Carbon;
+use Carbon\CarbonInterface;
 use ParagonIE\ConstantTime\Base64UrlSafe;
 use Statamic\Contracts\Auth\Passkey as Contract;
 use Statamic\Contracts\Auth\User as UserContract;
@@ -68,7 +69,7 @@ public function lastLogin(): ?Carbon
         return $this->lastLogin;
     }
 
-    public function setLastLogin(null|int|Carbon $time): Contract
+    public function setLastLogin(null|int|CarbonInterface $time): Contract
     {
         if ($time === null) {
             $this->lastLogin = null;
@@ -76,7 +77,7 @@ public function setLastLogin(null|int|Carbon $time): Contract
             return $this;
         }
 
-        $this->lastLogin = $time instanceof Carbon ? $time : Carbon::createFromTimestamp($time);
+        $this->lastLogin = is_int($time) ? Carbon::createFromTimestamp($time) : Carbon::instance($time);
 
         return $this;
     }
diff --git a/src/Contracts/Auth/Passkey.php b/src/Contracts/Auth/Passkey.php
index 81404728c10..6c93f6b1a23 100644
--- a/src/Contracts/Auth/Passkey.php
+++ b/src/Contracts/Auth/Passkey.php
@@ -3,6 +3,7 @@
 namespace Statamic\Contracts\Auth;
 
 use Carbon\Carbon;
+use Carbon\CarbonInterface;
 use Webauthn\PublicKeyCredentialSource;
 
 interface Passkey
@@ -23,7 +24,7 @@ public function setCredential(array|PublicKeyCredentialSource $credential): self
 
     public function lastLogin(): ?Carbon;
 
-    public function setLastLogin(null|int|Carbon $time): self;
+    public function setLastLogin(null|int|CarbonInterface $time): self;
 
     public function save(): bool;
 
diff --git a/tests/Auth/Eloquent/EloquentUserTest.php b/tests/Auth/Eloquent/EloquentUserTest.php
index 92520cf03d4..c001e1213a0 100644
--- a/tests/Auth/Eloquent/EloquentUserTest.php
+++ b/tests/Auth/Eloquent/EloquentUserTest.php
@@ -2,10 +2,14 @@
 
 namespace Tests\Auth\Eloquent;
 
+use Carbon\CarbonImmutable;
+use Carbon\CarbonInterface;
+use DateTime;
 use Illuminate\Filesystem\Filesystem;
 use Illuminate\Foundation\Testing\WithFaker;
 use Illuminate\Support\Carbon;
 use Illuminate\Support\Collection;
+use Illuminate\Support\Facades\Date;
 use ParagonIE\ConstantTime\Base64UrlSafe;
 use PHPUnit\Framework\Attributes\Group;
 use PHPUnit\Framework\Attributes\Test;
@@ -310,6 +314,27 @@ public function it_gets_the_timestamps_property_from_the_model()
         $this->assertFalse($user->timestamps);
     }
 
+    #[Test]
+    public function it_gets_the_last_login_when_the_app_uses_immutable_dates()
+    {
+        Date::use(CarbonImmutable::class);
+
+        // The Control Panel's Localize middleware changes the format too.
+        Date::setToStringFormat(DateTime::ATOM);
+
+        $this->beforeApplicationDestroyed(function () {
+            Date::useDefault();
+            Date::resetToStringFormat();
+        });
+
+        $user = $this->makeUser();
+        $user->model()->mergeCasts(['last_login' => 'datetime']);
+        $user->setLastLogin(now());
+
+        $this->assertInstanceOf(CarbonInterface::class, $user->lastLogin());
+        $this->assertEquals('2019-11-21 23:39:29', $user->lastLogin()->format('Y-m-d H:i:s'));
+    }
+
     #[Test]
     public function it_gets_super_correctly_on_the_model()
     {
diff --git a/tests/Auth/WebAuthn/EloquentPasskeyTest.php b/tests/Auth/WebAuthn/EloquentPasskeyTest.php
index 9bf27c38b5f..913737006d7 100644
--- a/tests/Auth/WebAuthn/EloquentPasskeyTest.php
+++ b/tests/Auth/WebAuthn/EloquentPasskeyTest.php
@@ -3,8 +3,10 @@
 namespace Tests\Auth\WebAuthn;
 
 use Carbon\Carbon;
+use Carbon\CarbonImmutable;
 use Illuminate\Filesystem\Filesystem;
 use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Support\Facades\Date;
 use ParagonIE\ConstantTime\Base64UrlSafe;
 use PHPUnit\Framework\Attributes\Group;
 use PHPUnit\Framework\Attributes\Test;
@@ -157,6 +159,26 @@ public function it_updates_existing_passkey()
         ]);
     }
 
+    #[Test]
+    public function it_saves_a_passkey_with_a_last_login_when_the_app_uses_immutable_dates()
+    {
+        Date::use(CarbonImmutable::class);
+
+        $this->beforeApplicationDestroyed(fn () => Date::useDefault());
+
+        $user = User::make()->email('test@example.com')->set('name', 'Test User');
+        $user->save();
+
+        $passkey = (new Passkey)
+            ->setName('My Passkey')
+            ->setUser($user)
+            ->setCredential($this->createTestCredential())
+            ->setLastLogin(now());
+
+        $this->assertTrue($passkey->save());
+        $this->assertEquals('2019-11-21 23:39:29', $passkey->lastLogin()->format('Y-m-d H:i:s'));
+    }
+
     #[Test]
     public function it_saves_multiple_passkeys_for_same_user()
     {
diff --git a/tests/Auth/WebAuthn/PasskeyTests.php b/tests/Auth/WebAuthn/PasskeyTests.php
index afa97c20f18..645f8fd6317 100644
--- a/tests/Auth/WebAuthn/PasskeyTests.php
+++ b/tests/Auth/WebAuthn/PasskeyTests.php
@@ -3,6 +3,7 @@
 namespace Tests\Auth\WebAuthn;
 
 use Carbon\Carbon;
+use Carbon\CarbonImmutable;
 use PHPUnit\Framework\Attributes\Test;
 use Statamic\Contracts\Auth\Passkey;
 use Statamic\Facades\User;
@@ -31,6 +32,22 @@ public function it_gets_last_login()
         $this->assertEquals('2024-01-15 10:30:00', $passkey->lastLogin()->format('Y-m-d H:i:s'));
     }
 
+    #[Test]
+    public function it_sets_last_login_from_an_immutable_date()
+    {
+        $user = tap(User::make()->email('test@example.com')->data(['name' => 'John Smith']))->save();
+        $credential = $this->createTestCredential();
+
+        $passkey = $this->newPasskey()
+            ->setName('My Passkey')
+            ->setUser($user)
+            ->setCredential($credential)
+            ->setLastLogin(CarbonImmutable::create(2024, 1, 15, 10, 30, 0));
+
+        $this->assertInstanceOf(Carbon::class, $passkey->lastLogin());
+        $this->assertEquals('2024-01-15 10:30:00', $passkey->lastLogin()->format('Y-m-d H:i:s'));
+    }
+
     #[Test]
     public function it_handles_null_last_login()
     {