diff --git a/migrations/Version20260623183021.php b/migrations/Version20260623183021.php
new file mode 100644
index 0000000..834c02e
--- /dev/null
+++ b/migrations/Version20260623183021.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace DoctrineMigrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+/**
+ * Auto-generated Migration: Please modify to your needs!
+ */
+final class Version20260623183021 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return '';
+    }
+
+    public function up(Schema $schema): void
+    {
+        // this up() migration is auto-generated, please modify it to your needs
+        $this->addSql('ALTER TABLE scenario ADD owner_id UUID NOT NULL');
+        $this->addSql('ALTER TABLE scenario ADD CONSTRAINT FK_3E45C8D87E3C61F9 FOREIGN KEY (owner_id) REFERENCES "user" (id) ON DELETE CASCADE NOT DEFERRABLE');
+        $this->addSql('CREATE INDEX IDX_3E45C8D87E3C61F9 ON scenario (owner_id)');
+    }
+
+    public function down(Schema $schema): void
+    {
+        // this down() migration is auto-generated, please modify it to your needs
+        $this->addSql('ALTER TABLE scenario DROP CONSTRAINT FK_3E45C8D87E3C61F9');
+        $this->addSql('DROP INDEX IDX_3E45C8D87E3C61F9');
+        $this->addSql('ALTER TABLE scenario DROP owner_id');
+    }
+}
diff --git a/src/Entity/Scenario.php b/src/Entity/Scenario.php
index 9d9abc1..adc33bc 100644
--- a/src/Entity/Scenario.php
+++ b/src/Entity/Scenario.php
@@ -24,6 +24,15 @@ class Scenario
     #[ORM\Column(type: 'uuid')]
     private UuidV7 $id;
 
+    /**
+     * Set server-side by App\State\ScenarioOwnerProcessor on write; must be
+     * assigned via setOwner() before persist. The non-nullable type means
+     * getOwner() throws if read before that invariant is satisfied.
+     */
+    #[ORM\ManyToOne(targetEntity: User::class)]
+    #[ORM\JoinColumn(nullable: false, onDelete: 'CASCADE')]
+    private User $owner;
+
     #[ORM\Column(enumType: DistributionMode::class)]
     private DistributionMode $distributionMode = DistributionMode::EVEN;
 
@@ -44,6 +53,11 @@ class Scenario
         return $this->id;
     }
 
+    public function getOwner(): User
+    {
+        return $this->owner;
+    }
+
     public function getDistributionMode(): DistributionMode
     {
         return $this->distributionMode;
@@ -59,6 +73,13 @@ class Scenario
         return $this->description;
     }
 
+    public function setOwner(User $owner): static
+    {
+        $this->owner = $owner;
+
+        return $this;
+    }
+
     public function setDistributionMode(DistributionMode $distributionMode): static
     {
         $this->distributionMode = $distributionMode;
diff --git a/src/State/ScenarioOwnerProcessor.php b/src/State/ScenarioOwnerProcessor.php
new file mode 100644
index 0000000..899ec9d
--- /dev/null
+++ b/src/State/ScenarioOwnerProcessor.php
@@ -0,0 +1,50 @@
+<?php
+
+namespace App\State;
+
+use ApiPlatform\Metadata\Operation;
+use ApiPlatform\State\ProcessorInterface;
+use App\Entity\Scenario;
+use App\Entity\User;
+use Symfony\Bundle\SecurityBundle\Security;
+use Symfony\Component\DependencyInjection\Attribute\AsDecorator;
+use Symfony\Component\DependencyInjection\Attribute\AutowireDecorated;
+
+/**
+ * Stamps the authenticated user as the owner of a Scenario on write,
+ * then hands off to the core Doctrine persist processor.
+ *
+ * @implements ProcessorInterface<object, object|null>
+ */
+#[AsDecorator('api_platform.doctrine.orm.state.persist_processor')]
+final class ScenarioOwnerProcessor implements ProcessorInterface
+{
+    /**
+     * @param ProcessorInterface<object, object|null> $decorated
+     */
+    public function __construct(
+        #[AutowireDecorated]
+        private readonly ProcessorInterface $decorated,
+        private readonly Security $security,
+    ) {
+    }
+
+    public function process(
+        mixed $data,
+        Operation $operation,
+        array $uriVariables = [],
+        array $context = [],
+    ): mixed {
+        if ($data instanceof Scenario) {
+            // The Scenario Post operation is gated by `is_granted('ROLE_USER')`
+            // (see #[ApiResource] on App\Entity\Scenario), so by the time this
+            // processor runs the security pipeline guarantees a logged-in User.
+            $user = $this->security->getUser();
+            \assert($user instanceof User);
+
+            $data->setOwner($user);
+        }
+
+        return $this->decorated->process($data, $operation, $uriVariables, $context);
+    }
+}
diff --git a/tests/Entity/BucketPersistenceTest.php b/tests/Entity/BucketPersistenceTest.php
index da4cf94..ac7d0a8 100644
--- a/tests/Entity/BucketPersistenceTest.php
+++ b/tests/Entity/BucketPersistenceTest.php
@@ -4,6 +4,7 @@ namespace App\Tests\Entity;
 
 use App\Entity\Bucket;
 use App\Entity\Scenario;
+use App\Entity\User;
 use App\Enum\BucketAllocationType;
 use App\Enum\BucketType;
 use Doctrine\DBAL\Exception\UniqueConstraintViolationException;
@@ -21,10 +22,25 @@ final class BucketPersistenceTest extends KernelTestCase
         $this->em = self::getContainer()->get(EntityManagerInterface::class);
     }
 
+    private function persistOwner(): User
+    {
+        static $counter = 0;
+        ++$counter;
+
+        $owner = new User();
+        $owner->setEmail(\sprintf('bucket-persistence-test-%d@example.com', $counter));
+        $owner->setPassword('irrelevant-hash');
+
+        $this->em->persist($owner);
+
+        return $owner;
+    }
+
     public function testItPersistsABucketLinkedToItsScenario(): void
     {
         $scenario = new Scenario();
         $scenario->setName('Household Budget');
+        $scenario->setOwner($this->persistOwner());
         $this->em->persist($scenario);
         $this->em->flush();
 
@@ -95,6 +111,7 @@ final class BucketPersistenceTest extends KernelTestCase
     {
         $scenario = new Scenario();
         $scenario->setName('Household Budget');
+        $scenario->setOwner($this->persistOwner());
         $this->em->persist($scenario);
         $this->em->flush();
 
@@ -134,6 +151,7 @@ final class BucketPersistenceTest extends KernelTestCase
     {
         $scenario = new Scenario();
         $scenario->setName('Household Budget');
+        $scenario->setOwner($this->persistOwner());
         $this->em->persist($scenario);
         $this->em->flush();
 
@@ -174,6 +192,7 @@ final class BucketPersistenceTest extends KernelTestCase
     {
         $scenario = new Scenario();
         $scenario->setName('Household Budget');
+        $scenario->setOwner($this->persistOwner());
         $this->em->persist($scenario);
         $this->em->flush();
 
diff --git a/tests/Entity/ScenarioOwnerTest.php b/tests/Entity/ScenarioOwnerTest.php
new file mode 100644
index 0000000..ad05883
--- /dev/null
+++ b/tests/Entity/ScenarioOwnerTest.php
@@ -0,0 +1,49 @@
+<?php
+
+namespace App\Tests\Entity;
+
+use App\Entity\Scenario;
+use App\Entity\User;
+use Doctrine\ORM\EntityManagerInterface;
+use Symfony\Bundle\FrameworkBundle\Test\KernelTestCase;
+
+final class ScenarioOwnerTest extends KernelTestCase
+{
+    private EntityManagerInterface $em;
+
+    protected function setUp(): void
+    {
+        self::bootKernel();
+        $this->em = self::getContainer()->get(EntityManagerInterface::class);
+    }
+
+    public function testOwnerRoundTripsThroughPersistence(): void
+    {
+        $owner = new User();
+        $owner->setEmail('scenario-owner-test@example.com');
+        $owner->setPassword('irrelevant-hash');
+
+        $this->em->persist($owner);
+
+        $scenario = new Scenario();
+        $scenario->setName('Household Budget');
+        $scenario->setOwner($owner);
+
+        $this->em->persist($scenario);
+        $this->em->flush();
+
+        $scenarioId = $scenario->getId();
+        $ownerId = $owner->getId();
+
+        $this->em->clear();
+
+        $reloaded = $this->em->find(Scenario::class, $scenarioId);
+
+        self::assertNotNull($reloaded, 'Scenario must be retrievable from the database after an identity-map clear.');
+        self::assertInstanceOf(User::class, $reloaded->getOwner());
+        self::assertTrue(
+            $ownerId->equals($reloaded->getOwner()->getId()),
+            'The owner set before persistence must survive a flush + clear + reload round-trip.',
+        );
+    }
+}
diff --git a/tests/Entity/ScenarioPersistenceTest.php b/tests/Entity/ScenarioPersistenceTest.php
index 3e56db4..3fee263 100644
--- a/tests/Entity/ScenarioPersistenceTest.php
+++ b/tests/Entity/ScenarioPersistenceTest.php
@@ -3,6 +3,7 @@
 namespace App\Tests\Entity;
 
 use App\Entity\Scenario;
+use App\Entity\User;
 use App\Enum\DistributionMode;
 use Doctrine\ORM\EntityManagerInterface;
 use Symfony\Bundle\FrameworkBundle\Test\KernelTestCase;
@@ -18,10 +19,25 @@ final class ScenarioPersistenceTest extends KernelTestCase
         $this->em = self::getContainer()->get(EntityManagerInterface::class);
     }
 
+    private function persistOwner(): User
+    {
+        static $counter = 0;
+        ++$counter;
+
+        $owner = new User();
+        $owner->setEmail(\sprintf('scenario-persistence-test-%d@example.com', $counter));
+        $owner->setPassword('irrelevant-hash');
+
+        $this->em->persist($owner);
+
+        return $owner;
+    }
+
     public function testItPersistsAScenarioWithAUuidId(): void
     {
         $scenario = new Scenario();
         $scenario->setName('Household Budget');
+        $scenario->setOwner($this->persistOwner());
 
         $this->em->persist($scenario);
         $this->em->flush();
@@ -42,6 +58,7 @@ final class ScenarioPersistenceTest extends KernelTestCase
     {
         $scenario = new Scenario();
         $scenario->setName('Default Mode Scenario');
+        $scenario->setOwner($this->persistOwner());
 
         $this->em->persist($scenario);
         $this->em->flush();
@@ -65,6 +82,7 @@ final class ScenarioPersistenceTest extends KernelTestCase
         $scenario = new Scenario();
         $scenario->setName('Priority Mode Scenario');
         $scenario->setDistributionMode(DistributionMode::PRIORITY);
+        $scenario->setOwner($this->persistOwner());
 
         $this->em->persist($scenario);
         $this->em->flush();
@@ -93,6 +111,7 @@ final class ScenarioPersistenceTest extends KernelTestCase
         $scenario = new Scenario();
         $scenario->setName('Described Scenario');
         $scenario->setDescription('Covers rent, groceries, and the emergency buffer.');
+        $scenario->setOwner($this->persistOwner());
 
         $this->em->persist($scenario);
         $this->em->flush();
@@ -111,6 +130,7 @@ final class ScenarioPersistenceTest extends KernelTestCase
     {
         $scenario = new Scenario();
         $scenario->setName('Undescribed Scenario');
+        $scenario->setOwner($this->persistOwner());
 
         $this->em->persist($scenario);
         $this->em->flush();
diff --git a/tests/Entity/StreamPersistenceTest.php b/tests/Entity/StreamPersistenceTest.php
index c94dbb1..9a4c2ae 100644
--- a/tests/Entity/StreamPersistenceTest.php
+++ b/tests/Entity/StreamPersistenceTest.php
@@ -5,6 +5,7 @@ namespace App\Tests\Entity;
 use App\Entity\Bucket;
 use App\Entity\Scenario;
 use App\Entity\Stream;
+use App\Entity\User;
 use App\Enum\BucketAllocationType;
 use App\Enum\BucketType;
 use App\Enum\StreamFrequency;
@@ -22,10 +23,25 @@ final class StreamPersistenceTest extends KernelTestCase
         $this->em = self::getContainer()->get(EntityManagerInterface::class);
     }
 
+    private function persistOwner(): User
+    {
+        static $counter = 0;
+        ++$counter;
+
+        $owner = new User();
+        $owner->setEmail(\sprintf('stream-persistence-test-%d@example.com', $counter));
+        $owner->setPassword('irrelevant-hash');
+
+        $this->em->persist($owner);
+
+        return $owner;
+    }
+
     public function testItPersistsAStreamLinkedToItsScenarioAndBucket(): void
     {
         $scenario = new Scenario();
         $scenario->setName('Household Budget');
+        $scenario->setOwner($this->persistOwner());
         $this->em->persist($scenario);
 
         $bucket = new Bucket();
@@ -119,6 +135,7 @@ final class StreamPersistenceTest extends KernelTestCase
     {
         $scenario = new Scenario();
         $scenario->setName('Household Budget');
+        $scenario->setOwner($this->persistOwner());
         $this->em->persist($scenario);
         $this->em->flush();
 
diff --git a/tests/Functional/BucketApiTest.php b/tests/Functional/BucketApiTest.php
index 2eed148..33897f5 100644
--- a/tests/Functional/BucketApiTest.php
+++ b/tests/Functional/BucketApiTest.php
@@ -22,6 +22,7 @@ final class BucketApiTest extends WebTestCase
 
     private KernelBrowser $client;
     private EntityManagerInterface $em;
+    private User $user;
 
     protected function setUp(): void
     {
@@ -36,11 +37,11 @@ final class BucketApiTest extends WebTestCase
         ]);
         $hasher = new UserPasswordHasher($factory);
 
-        $user = new User();
-        $user->setEmail(self::EMAIL);
-        $user->setPassword($hasher->hashPassword($user, self::PASSWORD));
+        $this->user = new User();
+        $this->user->setEmail(self::EMAIL);
+        $this->user->setPassword($hasher->hashPassword($this->user, self::PASSWORD));
 
-        $this->em->persist($user);
+        $this->em->persist($this->user);
         $this->em->flush();
     }
 
@@ -62,6 +63,7 @@ final class BucketApiTest extends WebTestCase
     {
         $scenario = new Scenario();
         $scenario->setName($name);
+        $scenario->setOwner($this->user);
 
         $this->em->persist($scenario);
         $this->em->flush();
diff --git a/tests/Functional/ProjectionPreviewApiTest.php b/tests/Functional/ProjectionPreviewApiTest.php
index 5447b33..110e399 100644
--- a/tests/Functional/ProjectionPreviewApiTest.php
+++ b/tests/Functional/ProjectionPreviewApiTest.php
@@ -27,6 +27,7 @@ final class ProjectionPreviewApiTest extends WebTestCase
 
     private KernelBrowser $client;
     private EntityManagerInterface $em;
+    private User $user;
 
     protected function setUp(): void
     {
@@ -41,11 +42,11 @@ final class ProjectionPreviewApiTest extends WebTestCase
         ]);
         $hasher = new UserPasswordHasher($factory);
 
-        $user = new User();
-        $user->setEmail(self::EMAIL);
-        $user->setPassword($hasher->hashPassword($user, self::PASSWORD));
+        $this->user = new User();
+        $this->user->setEmail(self::EMAIL);
+        $this->user->setPassword($hasher->hashPassword($this->user, self::PASSWORD));
 
-        $this->em->persist($user);
+        $this->em->persist($this->user);
         $this->em->flush();
     }
 
@@ -67,6 +68,7 @@ final class ProjectionPreviewApiTest extends WebTestCase
     {
         $scenario = new Scenario();
         $scenario->setName($name);
+        $scenario->setOwner($this->user);
 
         $this->em->persist($scenario);
         $this->em->flush();
diff --git a/tests/Functional/ScenarioApiTest.php b/tests/Functional/ScenarioApiTest.php
index 56ff79a..d0f58d2 100644
--- a/tests/Functional/ScenarioApiTest.php
+++ b/tests/Functional/ScenarioApiTest.php
@@ -18,6 +18,7 @@ final class ScenarioApiTest extends WebTestCase
 
     private KernelBrowser $client;
     private EntityManagerInterface $em;
+    private User $user;
 
     protected function setUp(): void
     {
@@ -32,11 +33,11 @@ final class ScenarioApiTest extends WebTestCase
         ]);
         $hasher = new UserPasswordHasher($factory);
 
-        $user = new User();
-        $user->setEmail(self::EMAIL);
-        $user->setPassword($hasher->hashPassword($user, self::PASSWORD));
+        $this->user = new User();
+        $this->user->setEmail(self::EMAIL);
+        $this->user->setPassword($hasher->hashPassword($this->user, self::PASSWORD));
 
-        $this->em->persist($user);
+        $this->em->persist($this->user);
         $this->em->flush();
     }
 
@@ -58,6 +59,7 @@ final class ScenarioApiTest extends WebTestCase
     {
         $scenario = new Scenario();
         $scenario->setName($name);
+        $scenario->setOwner($this->user);
 
         $this->em->persist($scenario);
         $this->em->flush();
diff --git a/tests/Functional/ScenarioOwnerApiTest.php b/tests/Functional/ScenarioOwnerApiTest.php
new file mode 100644
index 0000000..367fc12
--- /dev/null
+++ b/tests/Functional/ScenarioOwnerApiTest.php
@@ -0,0 +1,156 @@
+<?php
+
+namespace App\Tests\Functional;
+
+use App\Entity\User;
+use Doctrine\ORM\EntityManagerInterface;
+use Symfony\Bundle\FrameworkBundle\KernelBrowser;
+use Symfony\Bundle\FrameworkBundle\Test\WebTestCase;
+use Symfony\Component\PasswordHasher\Hasher\NativePasswordHasher;
+use Symfony\Component\PasswordHasher\Hasher\PasswordHasherFactory;
+use Symfony\Component\PasswordHasher\Hasher\UserPasswordHasher;
+
+final class ScenarioOwnerApiTest extends WebTestCase
+{
+    private const EMAIL = 'scenario-owner-api-test@example.com';
+    private const PASSWORD = 'correct-horse-battery-staple';
+
+    private const OTHER_EMAIL = 'scenario-owner-api-spoof-target@example.com';
+
+    private KernelBrowser $client;
+    private EntityManagerInterface $em;
+    private User $caller;
+    private User $otherUser;
+
+    protected function setUp(): void
+    {
+        $this->client = static::createClient();
+
+        /** @var EntityManagerInterface $em */
+        $em = static::getContainer()->get(EntityManagerInterface::class);
+        $this->em = $em;
+
+        $factory = new PasswordHasherFactory([
+            User::class => new NativePasswordHasher(cost: 4),
+        ]);
+        $hasher = new UserPasswordHasher($factory);
+
+        $this->caller = new User();
+        $this->caller->setEmail(self::EMAIL);
+        $this->caller->setPassword($hasher->hashPassword($this->caller, self::PASSWORD));
+        $this->em->persist($this->caller);
+
+        $this->otherUser = new User();
+        $this->otherUser->setEmail(self::OTHER_EMAIL);
+        $this->otherUser->setPassword($hasher->hashPassword($this->otherUser, 'some-other-password'));
+        $this->em->persist($this->otherUser);
+
+        $this->em->flush();
+    }
+
+    private function login(): void
+    {
+        $this->client->jsonRequest('POST', '/api/login', [
+            'username' => self::EMAIL,
+            'password' => self::PASSWORD,
+        ]);
+
+        self::assertLessThan(
+            300,
+            $this->client->getResponse()->getStatusCode(),
+            'Test setup precondition: login must succeed before exercising the Scenario API.',
+        );
+    }
+
+    public function testPostCreatesAScenarioOwnedByTheAuthenticatedUser(): void
+    {
+        $this->login();
+
+        $this->client->request(
+            'POST',
+            '/api/scenarios',
+            server: [
+                'CONTENT_TYPE' => 'application/ld+json',
+                'HTTP_ACCEPT' => 'application/ld+json',
+            ],
+            content: json_encode(['name' => 'Holiday Fund']),
+        );
+
+        self::assertSame(
+            201,
+            $this->client->getResponse()->getStatusCode(),
+            'POST /api/scenarios with a valid body must return 201 Created.',
+        );
+
+        $this->em->clear();
+
+        $persisted = $this->em->getRepository(\App\Entity\Scenario::class)->findOneBy(['name' => 'Holiday Fund']);
+
+        self::assertNotNull($persisted, 'A successful POST /api/scenarios must persist the new Scenario.');
+        self::assertNotNull($persisted->getOwner(), 'The persisted Scenario must have an owner set.');
+        self::assertTrue(
+            $this->caller->getId()->equals($persisted->getOwner()->getId()),
+            'The persisted Scenario must be owned by the authenticated caller, not left null or assigned elsewhere.',
+        );
+    }
+
+    public function testPostIgnoresAClientSuppliedOwner(): void
+    {
+        $this->login();
+
+        $this->client->request(
+            'POST',
+            '/api/scenarios',
+            server: [
+                'CONTENT_TYPE' => 'application/ld+json',
+                'HTTP_ACCEPT' => 'application/ld+json',
+            ],
+            content: json_encode([
+                'name' => 'Spoofed Owner Fund',
+                'owner' => '/api/users/'.$this->otherUser->getId(),
+            ]),
+        );
+
+        self::assertSame(
+            201,
+            $this->client->getResponse()->getStatusCode(),
+            'POST /api/scenarios with a valid body must return 201 Created even when a client-supplied owner is present in the payload.',
+        );
+
+        $this->em->clear();
+
+        $persisted = $this->em->getRepository(\App\Entity\Scenario::class)->findOneBy(['name' => 'Spoofed Owner Fund']);
+
+        self::assertNotNull($persisted, 'A successful POST /api/scenarios must persist the new Scenario.');
+        self::assertNotNull($persisted->getOwner(), 'The persisted Scenario must have an owner set.');
+        self::assertTrue(
+            $this->caller->getId()->equals($persisted->getOwner()->getId()),
+            'A client-supplied owner in the request body must be ignored — the owner must always be the authenticated caller.',
+        );
+        self::assertFalse(
+            $this->otherUser->getId()->equals($persisted->getOwner()->getId()),
+            'The spoofed owner IRI in the request body must never be honoured.',
+        );
+    }
+
+    public function testPostWithMissingNameIsStillRejectedAsUnprocessable(): void
+    {
+        $this->login();
+
+        $this->client->request(
+            'POST',
+            '/api/scenarios',
+            server: [
+                'CONTENT_TYPE' => 'application/ld+json',
+                'HTTP_ACCEPT' => 'application/ld+json',
+            ],
+            content: json_encode([]),
+        );
+
+        self::assertSame(
+            422,
+            $this->client->getResponse()->getStatusCode(),
+            'POST /api/scenarios without a name must still return 422 Unprocessable Entity — the owner-setting persist processor must not interfere with existing validation order.',
+        );
+    }
+}
diff --git a/tests/Functional/StreamApiTest.php b/tests/Functional/StreamApiTest.php
index f145fcd..f9e9f41 100644
--- a/tests/Functional/StreamApiTest.php
+++ b/tests/Functional/StreamApiTest.php
@@ -22,6 +22,7 @@ final class StreamApiTest extends WebTestCase
 
     private KernelBrowser $client;
     private EntityManagerInterface $em;
+    private User $user;
 
     protected function setUp(): void
     {
@@ -36,11 +37,11 @@ final class StreamApiTest extends WebTestCase
         ]);
         $hasher = new UserPasswordHasher($factory);
 
-        $user = new User();
-        $user->setEmail(self::EMAIL);
-        $user->setPassword($hasher->hashPassword($user, self::PASSWORD));
+        $this->user = new User();
+        $this->user->setEmail(self::EMAIL);
+        $this->user->setPassword($hasher->hashPassword($this->user, self::PASSWORD));
 
-        $this->em->persist($user);
+        $this->em->persist($this->user);
         $this->em->flush();
     }
 
@@ -62,6 +63,7 @@ final class StreamApiTest extends WebTestCase
     {
         $scenario = new Scenario();
         $scenario->setName($name);
+        $scenario->setOwner($this->user);
 
         $this->em->persist($scenario);
         $this->em->flush();
diff --git a/tests/Repository/BucketRepositoryTest.php b/tests/Repository/BucketRepositoryTest.php
index ca9ba6f..6670cc6 100644
--- a/tests/Repository/BucketRepositoryTest.php
+++ b/tests/Repository/BucketRepositoryTest.php
@@ -4,6 +4,7 @@ namespace App\Tests\Repository;
 
 use App\Entity\Bucket;
 use App\Entity\Scenario;
+use App\Entity\User;
 use App\Enum\BucketAllocationType;
 use App\Enum\BucketType;
 use App\Repository\BucketRepository;
@@ -141,8 +142,17 @@ final class BucketRepositoryTest extends KernelTestCase
 
     private function persistScenario(string $name = 'Household Budget'): Scenario
     {
+        static $counter = 0;
+        ++$counter;
+
+        $owner = new User();
+        $owner->setEmail(\sprintf('bucket-repository-test-%d@example.com', $counter));
+        $owner->setPassword('irrelevant-hash');
+        $this->em->persist($owner);
+
         $scenario = new Scenario();
         $scenario->setName($name);
+        $scenario->setOwner($owner);
         $this->em->persist($scenario);
         $this->em->flush();
 
diff --git a/tests/Validator/SingleOverflowPerScenarioTest.php b/tests/Validator/SingleOverflowPerScenarioTest.php
index 1d07767..d9ac68f 100644
--- a/tests/Validator/SingleOverflowPerScenarioTest.php
+++ b/tests/Validator/SingleOverflowPerScenarioTest.php
@@ -4,6 +4,7 @@ namespace App\Tests\Validator;
 
 use App\Entity\Bucket;
 use App\Entity\Scenario;
+use App\Entity\User;
 use App\Enum\BucketAllocationType;
 use App\Enum\BucketType;
 use App\Validator\SingleOverflowPerScenario;
@@ -24,10 +25,25 @@ final class SingleOverflowPerScenarioTest extends KernelTestCase
         $this->validator = self::getContainer()->get(ValidatorInterface::class);
     }
 
+    private function persistOwner(): User
+    {
+        static $counter = 0;
+        ++$counter;
+
+        $owner = new User();
+        $owner->setEmail(\sprintf('single-overflow-per-scenario-test-%d@example.com', $counter));
+        $owner->setPassword('irrelevant-hash');
+
+        $this->em->persist($owner);
+
+        return $owner;
+    }
+
     public function testSecondOverflowBucketOnTheSameScenarioRaisesAViolation(): void
     {
         $scenario = new Scenario();
         $scenario->setName('Household Budget');
+        $scenario->setOwner($this->persistOwner());
         $this->em->persist($scenario);
         $this->em->flush();
 
@@ -54,6 +70,7 @@ final class SingleOverflowPerScenarioTest extends KernelTestCase
     {
         $scenario = new Scenario();
         $scenario->setName('Household Budget');
+        $scenario->setOwner($this->persistOwner());
         $this->em->persist($scenario);
         $this->em->flush();
 
@@ -77,6 +94,7 @@ final class SingleOverflowPerScenarioTest extends KernelTestCase
     {
         $scenario = new Scenario();
         $scenario->setName('Household Budget');
+        $scenario->setOwner($this->persistOwner());
         $this->em->persist($scenario);
         $this->em->flush();