diff --git a/Neos.Neos/Classes/Domain/Repository/WorkspaceMetadataAndRoleRepository.php b/Neos.Neos/Classes/Domain/Repository/WorkspaceMetadataAndRoleRepository.php
index aabe268cae3..ba487eae2e7 100644
--- a/Neos.Neos/Classes/Domain/Repository/WorkspaceMetadataAndRoleRepository.php
+++ b/Neos.Neos/Classes/Domain/Repository/WorkspaceMetadataAndRoleRepository.php
@@ -340,7 +340,7 @@ public function addWorkspaceMetadata(ContentRepositoryId $contentRepositoryId, W
         }
     }
 
-    public function findPrimaryWorkspaceNameForUser(ContentRepositoryId $contentRepositoryId, UserId $userId): ?WorkspaceName
+    public function findWorkspaceNameByUser(ContentRepositoryId $contentRepositoryId, UserId $userId): ?WorkspaceName
     {
         $tableMetadata = self::TABLE_NAME_WORKSPACE_METADATA;
         $query = <<<SQL
@@ -353,8 +353,6 @@ public function findPrimaryWorkspaceNameForUser(ContentRepositoryId $contentRepo
                 AND classification = :personalWorkspaceClassification
                 AND owner_user_id = :userId
         SQL;
-        // We don't order the results and return the first matching workspace.
-        // In case multiple exist - which is not desired currently - and in the happy path not possible via the api (race conditions aside) - the order is not defined.
         $workspaceName = $this->dbal->fetchOne($query, [
             'contentRepositoryId' => $contentRepositoryId->value,
             'personalWorkspaceClassification' => WorkspaceClassification::PERSONAL->value,
diff --git a/Neos.Neos/Classes/Domain/Service/WorkspaceService.php b/Neos.Neos/Classes/Domain/Service/WorkspaceService.php
index 0b0f63390a4..578f39b7a25 100644
--- a/Neos.Neos/Classes/Domain/Service/WorkspaceService.php
+++ b/Neos.Neos/Classes/Domain/Service/WorkspaceService.php
@@ -101,7 +101,7 @@ public function setWorkspaceDescription(ContentRepositoryId $contentRepositoryId
      */
     public function getPersonalWorkspaceForUser(ContentRepositoryId $contentRepositoryId, UserId $userId): Workspace
     {
-        $workspaceName = $this->metadataAndRoleRepository->findPrimaryWorkspaceNameForUser($contentRepositoryId, $userId);
+        $workspaceName = $this->metadataAndRoleRepository->findWorkspaceNameByUser($contentRepositoryId, $userId);
         if ($workspaceName === null) {
             throw new \RuntimeException(sprintf('No workspace is assigned to the user with id "%s")', $userId->value), 1718293801);
         }
@@ -143,7 +143,7 @@ public function createRootWorkspace(ContentRepositoryId $contentRepositoryId, Wo
      */
     public function createPersonalWorkspace(ContentRepositoryId $contentRepositoryId, WorkspaceName $workspaceName, WorkspaceTitle $title, WorkspaceDescription $description, WorkspaceName $baseWorkspaceName, UserId $ownerId): void
     {
-        $existingUserWorkspace = $this->metadataAndRoleRepository->findPrimaryWorkspaceNameForUser($contentRepositoryId, $ownerId);
+        $existingUserWorkspace = $this->metadataAndRoleRepository->findWorkspaceNameByUser($contentRepositoryId, $ownerId);
         if ($existingUserWorkspace !== null) {
             throw new \RuntimeException(sprintf('Failed to create personal workspace "%s" for user with id "%s", because the workspace "%s" is already assigned to the user', $workspaceName->value, $ownerId->value, $existingUserWorkspace->value), 1733754904);
         }
@@ -193,7 +193,7 @@ public function createSharedWorkspace(ContentRepositoryId $contentRepositoryId,
      */
     public function createPersonalWorkspaceForUserIfMissing(ContentRepositoryId $contentRepositoryId, User $user): void
     {
-        $existingWorkspaceName = $this->metadataAndRoleRepository->findPrimaryWorkspaceNameForUser($contentRepositoryId, $user->getId());
+        $existingWorkspaceName = $this->metadataAndRoleRepository->findWorkspaceNameByUser($contentRepositoryId, $user->getId());
         if ($existingWorkspaceName !== null) {
             $this->requireWorkspace($contentRepositoryId, $existingWorkspaceName);
             return;
diff --git a/Neos.Neos/Migrations/Mysql/Version20240425223900.php b/Neos.Neos/Migrations/Mysql/Version20240425223900.php
index 69bd0305bcd..aca3a3a172a 100644
--- a/Neos.Neos/Migrations/Mysql/Version20240425223900.php
+++ b/Neos.Neos/Migrations/Mysql/Version20240425223900.php
@@ -29,7 +29,7 @@ public function up(Schema $schema): void
         $tableWorkspaceMetadata->addColumn('classification', 'string', ['length' => 255]);
         $tableWorkspaceMetadata->addColumn('owner_user_id', 'string', ['length' => 255, 'notnull' => false]);
         $tableWorkspaceMetadata->setPrimaryKey(['content_repository_id', 'workspace_name']);
-        $tableWorkspaceMetadata->addIndex(['owner_user_id']);
+        $tableWorkspaceMetadata->addIndex(['owner_user_id'], 'IDX_D6197E562B18554A');
 
         $tableWorkspaceRole = $schema->createTable('neos_neos_workspace_role');
         $tableWorkspaceRole->addColumn('content_repository_id', 'string', ['length' => 16]);
diff --git a/Neos.Neos/Migrations/Mysql/Version20241212000000.php b/Neos.Neos/Migrations/Mysql/Version20241212000000.php
new file mode 100644
index 00000000000..260398ed844
--- /dev/null
+++ b/Neos.Neos/Migrations/Mysql/Version20241212000000.php
@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Neos\Flow\Persistence\Doctrine\Migrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+final class Version20241212000000 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Restricts that the owner_user_id of the neos workspace metadata is unique';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->abortIf(
+            !$this->connection->getDatabasePlatform() instanceof \Doctrine\DBAL\Platforms\MariaDBPlatform,
+            "Migration can only be executed safely on '\Doctrine\DBAL\Platforms\MariaDBPlatform'."
+        );
+
+        $tableWorkspaceMetadata = $schema->getTable('neos_neos_workspace_metadata');
+        $tableWorkspaceMetadata->addUniqueIndex(['content_repository_id', 'owner_user_id'], 'owner');
+        $tableWorkspaceMetadata->dropIndex('IDX_D6197E562B18554A');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->abortIf(
+            !$this->connection->getDatabasePlatform() instanceof \Doctrine\DBAL\Platforms\MariaDBPlatform,
+            "Migration can only be executed safely on '\Doctrine\DBAL\Platforms\MariaDBPlatform'."
+        );
+
+        $tableWorkspaceMetadata = $schema->getTable('neos_neos_workspace_metadata');
+        $tableWorkspaceMetadata->addIndex(['owner_user_id'], 'IDX_D6197E562B18554A');
+        $tableWorkspaceMetadata->dropIndex('owner');
+    }
+}
diff --git a/Neos.Neos/Migrations/Postgresql/Version20240425223901.php b/Neos.Neos/Migrations/Postgresql/Version20240425223901.php
index b370bd7b9d1..93cb4813b24 100644
--- a/Neos.Neos/Migrations/Postgresql/Version20240425223901.php
+++ b/Neos.Neos/Migrations/Postgresql/Version20240425223901.php
@@ -26,7 +26,7 @@ public function up(Schema $schema): void
         $tableWorkspaceMetadata->addColumn('classification', 'string', ['length' => 255]);
         $tableWorkspaceMetadata->addColumn('owner_user_id', 'string', ['length' => 255, 'notnull' => false]);
         $tableWorkspaceMetadata->setPrimaryKey(['content_repository_id', 'workspace_name']);
-        $tableWorkspaceMetadata->addIndex(['owner_user_id']);
+        $tableWorkspaceMetadata->addIndex(['owner_user_id'], 'IDX_D6197E562B18554A');
 
         $tableWorkspaceRole = $schema->createTable('neos_neos_workspace_role');
         $tableWorkspaceRole->addColumn('content_repository_id', 'string', ['length' => 16]);
diff --git a/Neos.Neos/Migrations/Postgresql/Version20241212000001.php b/Neos.Neos/Migrations/Postgresql/Version20241212000001.php
new file mode 100644
index 00000000000..85e574c2969
--- /dev/null
+++ b/Neos.Neos/Migrations/Postgresql/Version20241212000001.php
@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Neos\Flow\Persistence\Doctrine\Migrations;
+
+use Doctrine\DBAL\Schema\Schema;
+use Doctrine\Migrations\AbstractMigration;
+
+final class Version20241212000001 extends AbstractMigration
+{
+    public function getDescription(): string
+    {
+        return 'Restricts that the owner_user_id of the neos workspace metadata is unique';
+    }
+
+    public function up(Schema $schema): void
+    {
+        $this->abortIf(
+            !$this->connection->getDatabasePlatform() instanceof \Doctrine\DBAL\Platforms\PostgreSQLPlatform,
+            "Migration can only be executed safely on '\Doctrine\DBAL\Platforms\PostgreSQLPlatform'."
+        );
+
+        $tableWorkspaceMetadata = $schema->getTable('neos_neos_workspace_metadata');
+        $tableWorkspaceMetadata->addUniqueIndex(['content_repository_id', 'owner_user_id'], 'owner');
+        $tableWorkspaceMetadata->dropIndex('IDX_D6197E562B18554A');
+    }
+
+    public function down(Schema $schema): void
+    {
+        $this->abortIf(
+            !$this->connection->getDatabasePlatform() instanceof \Doctrine\DBAL\Platforms\PostgreSQLPlatform,
+            "Migration can only be executed safely on '\Doctrine\DBAL\Platforms\PostgreSQLPlatform'."
+        );
+
+        $tableWorkspaceMetadata = $schema->getTable('neos_neos_workspace_metadata');
+        $tableWorkspaceMetadata->addIndex(['owner_user_id'], 'IDX_D6197E562B18554A');
+        $tableWorkspaceMetadata->dropIndex('owner');
+    }
+}