diff --git a/lib/API/JSON/v1/CustomFields.php b/lib/API/JSON/v1/CustomFields.php
index 736e451fbc..2c896c0191 100644
--- a/lib/API/JSON/v1/CustomFields.php
+++ b/lib/API/JSON/v1/CustomFields.php
@@ -4,7 +4,11 @@ namespace MailPoet\API\JSON\v1;
 
 use MailPoet\API\JSON\Endpoint as APIEndpoint;
 use MailPoet\API\JSON\Error as APIError;
+use MailPoet\API\JSON\Response;
+use MailPoet\API\JSON\ResponseBuilders\CustomFieldsResponseBuilder;
 use MailPoet\Config\AccessControl;
+use MailPoet\CustomFields\CustomFieldsRepository;
+use MailPoet\Entities\CustomFieldEntity;
 use MailPoet\Models\CustomField;
 use MailPoet\WP\Functions as WPFunctions;
 
@@ -13,22 +17,33 @@ class CustomFields extends APIEndpoint {
     'global' => AccessControl::PERMISSION_MANAGE_FORMS,
   ];
 
-  function getAll() {
-    $collection = CustomField::orderByAsc('created_at')->findMany();
-    $custom_fields = array_map(function($custom_field) {
-      return $custom_field->asArray();
-    }, $collection);
+  /** @var CustomFieldsRepository */
+  private $custom_fields_repository;
 
-    return $this->successResponse($custom_fields);
+  /** @var CustomFieldsResponseBuilder */
+  private $custom_fields_response_builder;
+
+  public function __construct(
+    CustomFieldsRepository $custom_fields_repository,
+    CustomFieldsResponseBuilder $custom_fields_response_builder
+  ) {
+    $this->custom_fields_repository = $custom_fields_repository;
+    $this->custom_fields_response_builder = $custom_fields_response_builder;
+  }
+
+  function getAll() {
+    $collection = $this->custom_fields_repository->findBy([], ['created_at' => 'asc']);
+    return $this->successResponse($this->custom_fields_response_builder->buildBatch($collection));
   }
 
   function delete($data = []) {
     $id = (isset($data['id']) ? (int)$data['id'] : null);
-    $custom_field = CustomField::findOne($id);
-    if ($custom_field instanceof CustomField) {
-      $custom_field->delete();
+    $custom_field = $this->custom_fields_repository->findOneById($id);
+    if ($custom_field instanceof CustomFieldEntity) {
+      $this->custom_fields_repository->remove($custom_field);
+      $this->custom_fields_repository->flush();
 
-      return $this->successResponse($custom_field->asArray());
+      return $this->successResponse($this->custom_fields_response_builder->build($custom_field));
     } else {
       return $this->errorResponse([
         APIError::NOT_FOUND => WPFunctions::get()->__('This custom field does not exist.', 'mailpoet'),
@@ -37,24 +52,21 @@ class CustomFields extends APIEndpoint {
   }
 
   function save($data = []) {
-    $custom_field = CustomField::createOrUpdate($data);
-    $errors = $custom_field->getErrors();
-
-    if (!empty($errors)) {
-      return $this->badRequest($errors);
+    try {
+      $custom_field = $this->custom_fields_repository->createOrUpdate($data);
+      $custom_field = $this->custom_fields_repository->findOneById($custom_field->getId());
+      if(!$custom_field instanceof CustomFieldEntity) return $this->errorResponse();
+      return $this->successResponse($this->custom_fields_response_builder->build($custom_field));
+    } catch (\Exception $e) {
+      return $this->errorResponse($errors = [], $meta = [], $status = Response::STATUS_BAD_REQUEST);
     }
-    $custom_field = CustomField::findOne($custom_field->id);
-    if(!$custom_field instanceof CustomField) return $this->errorResponse();
-    $response = $custom_field->asArray();
-    $response['id'] = (int)$response['id'];
-    return $this->successResponse($response);
   }
 
   function get($data = []) {
     $id = (isset($data['id']) ? (int)$data['id'] : null);
-    $custom_field = CustomField::findOne($id);
-    if ($custom_field instanceof CustomField) {
-      return $this->successResponse($custom_field->asArray());
+    $custom_field = $this->custom_fields_repository->findOneById($id);
+    if ($custom_field instanceof CustomFieldEntity) {
+      return $this->successResponse($this->custom_fields_response_builder->build($custom_field));
     }
     return $this->errorResponse([
       APIError::NOT_FOUND => WPFunctions::get()->__('This custom field does not exist.', 'mailpoet'),
diff --git a/lib/CustomFields/CustomFieldsRepository.php b/lib/CustomFields/CustomFieldsRepository.php
index cc4b888b03..a849e2659d 100644
--- a/lib/CustomFields/CustomFieldsRepository.php
+++ b/lib/CustomFields/CustomFieldsRepository.php
@@ -17,4 +17,25 @@ class CustomFieldsRepository extends Repository {
   protected function getEntityClassName() {
     return CustomFieldEntity::class;
   }
+
+  /**
+   * @param array $data
+   * @return CustomFieldEntity
+   */
+  public function createOrUpdate($data) {
+    if (isset($data['id'])) {
+      $field = $this->findOneById((int)$data['id']);
+    } elseif (isset($data['name'])) {
+      $field = $this->findOneBy(['name' => $data['name']]);
+    }
+    if (!isset($field)) {
+      $field = new CustomFieldEntity();
+      $this->entity_manager->persist($field);
+    }
+    if (isset($data['name'])) $field->setName($data['name']);
+    if (isset($data['type'])) $field->setType($data['type']);
+    if (isset($data['params'])) $field->setParams($data['params']);
+    $this->entity_manager->flush();
+    return $field;
+  }
 }
diff --git a/lib/Entities/CustomFieldEntity.php b/lib/Entities/CustomFieldEntity.php
index 803940d5a2..6c8498d689 100644
--- a/lib/Entities/CustomFieldEntity.php
+++ b/lib/Entities/CustomFieldEntity.php
@@ -20,19 +20,20 @@ class CustomFieldEntity {
 
   /**
    * @ORM\Column(type="string", nullable=false, unique=true)
+   * @Assert\NotBlank()
    * @var string
    */
   private $name;
 
   /**
    * @ORM\Column(type="string", nullable=false)
+   * @Assert\NotBlank()
    * @var string
    */
   private $type;
 
   /**
    * @ORM\Column(type="json_or_serialized")
-   * @Assert\NotBlank()
    * @var array
    */
   private $params;
@@ -57,4 +58,25 @@ class CustomFieldEntity {
   public function getParams() {
     return $this->params;
   }
+
+  /**
+   * @param string $name
+   */
+  public function setName($name) {
+    $this->name = $name;
+  }
+
+  /**
+   * @param string $type
+   */
+  public function setType($type) {
+    $this->type = $type;
+  }
+
+  /**
+   * @param array $params
+   */
+  public function setParams($params) {
+    $this->params = $params;
+  }
 }
diff --git a/tests/integration/API/JSON/v1/CustomFieldsTest.php b/tests/integration/API/JSON/v1/CustomFieldsTest.php
index cdc4adc2ff..b136bdfa39 100644
--- a/tests/integration/API/JSON/v1/CustomFieldsTest.php
+++ b/tests/integration/API/JSON/v1/CustomFieldsTest.php
@@ -3,10 +3,17 @@
 namespace MailPoet\Test\API\JSON\v1;
 
 use MailPoet\API\JSON\Response as APIResponse;
+use MailPoet\API\JSON\ResponseBuilders\CustomFieldsResponseBuilder;
 use MailPoet\API\JSON\v1\CustomFields;
+use MailPoet\CustomFields\CustomFieldsRepository;
+use MailPoet\DI\ContainerWrapper;
 use MailPoet\Models\CustomField;
 
 class CustomFieldsTest extends \MailPoetTest {
+
+  /** @var CustomFieldsRepository */
+  private $repository;
+
   private $custom_fields = [
     [
       'name' => 'CF: text',
@@ -54,13 +61,15 @@ class CustomFieldsTest extends \MailPoetTest {
 
   function _before() {
     parent::_before();
+    $this->repository = ContainerWrapper::getInstance(WP_DEBUG)->get(CustomFieldsRepository::class);
+    $this->repository->truncate();
     foreach ($this->custom_fields as $custom_field) {
-      CustomField::createOrUpdate($custom_field);
+      $this->repository->createOrUpdate($custom_field);
     }
   }
 
   function testItCanGetAllCustomFields() {
-    $router = new CustomFields();
+    $router = new CustomFields($this->repository, new CustomFieldsResponseBuilder());
     $response = $router->getAll();
     expect($response->status)->equals(APIResponse::STATUS_OK);
     expect($response->data)->count(count($this->custom_fields));
@@ -76,7 +85,7 @@ class CustomFieldsTest extends \MailPoetTest {
     $custom_field = CustomField::where('type', 'date')->findOne();
     $custom_field_id = $custom_field->id();
 
-    $router = new CustomFields();
+    $router = new CustomFields($this->repository, new CustomFieldsResponseBuilder());
     $response = $router->delete(['id' => $custom_field_id]);
     expect($response->status)->equals(APIResponse::STATUS_OK);
 
@@ -91,34 +100,31 @@ class CustomFieldsTest extends \MailPoetTest {
     $new_custom_field = [
       'name' => 'New custom field',
       'type' => 'text',
+      'params' => [],
     ];
 
-    $router = new CustomFields();
+    $router = new CustomFields($this->repository, new CustomFieldsResponseBuilder());
     $response = $router->save($new_custom_field);
     expect($response->status)->equals(APIResponse::STATUS_OK);
 
     // missing type
-    $response = $router->save(['name' => 'New custom field']);
+    $response = $router->save(['name' => 'New custom field1']);
     expect($response->status)->equals(APIResponse::STATUS_BAD_REQUEST);
-    expect($response->errors[0]['message'])->equals('Please specify a type.');
 
     // missing name
     $response = $router->save(['type' => 'text']);
     expect($response->status)->equals(APIResponse::STATUS_BAD_REQUEST);
-    expect($response->errors[0]['message'])->equals('Please specify a name.');
 
     // missing data
     $response = $router->save();
     expect($response->status)->equals(APIResponse::STATUS_BAD_REQUEST);
-    expect($response->errors[0]['message'])->equals('Please specify a name.');
-    expect($response->errors[1]['message'])->equals('Please specify a type.');
   }
 
   function testItCanGetACustomField() {
-    $custom_field = CustomField::where('name', 'CF: text')->findOne();
+    $custom_field = $this->repository->findOneBy(['name' => 'CF: text']);
 
-    $router = new CustomFields();
-    $response = $router->get(['id' => $custom_field->id()]);
+    $router = new CustomFields($this->repository, new CustomFieldsResponseBuilder());
+    $response = $router->get(['id' => $custom_field->getId()]);
 
     expect($response->data['name'])->equals('CF: text');
     expect($response->data['type'])->equals('text');
@@ -127,8 +133,4 @@ class CustomFieldsTest extends \MailPoetTest {
     $response = $router->get(['id' => 'not_an_id']);
     expect($response->status)->equals(APIResponse::STATUS_NOT_FOUND);
   }
-
-  function _after() {
-    CustomField::deleteMany();
-  }
 }