diff --git a/lib/API/JSON/v1/Subscribers.php b/lib/API/JSON/v1/Subscribers.php
index 4608b8663b..39b69590ee 100644
--- a/lib/API/JSON/v1/Subscribers.php
+++ b/lib/API/JSON/v1/Subscribers.php
@@ -68,6 +68,9 @@ class Subscribers extends APIEndpoint {
   /** @var SubscriptionUrlFactory */
   private $subscriptionUrlFactory;
 
+  /** @var FieldNameObfuscator */
+  private $fieldNameObfuscator;
+
   public function __construct(
     Listing\BulkActionController $bulkActionController,
     SubscribersListings $subscribersListings,
@@ -79,7 +82,8 @@ class Subscribers extends APIEndpoint {
     SettingsController $settings,
     CaptchaSession $captchaSession,
     ConfirmationEmailMailer $confirmationEmailMailer,
-    SubscriptionUrlFactory $subscriptionUrlFactory
+    SubscriptionUrlFactory $subscriptionUrlFactory,
+    FieldNameObfuscator $fieldNameObfuscator
   ) {
     $this->bulkActionController = $bulkActionController;
     $this->subscribersListings = $subscribersListings;
@@ -92,6 +96,7 @@ class Subscribers extends APIEndpoint {
     $this->captchaSession = $captchaSession;
     $this->confirmationEmailMailer = $confirmationEmailMailer;
     $this->subscriptionUrlFactory = $subscriptionUrlFactory;
+    $this->fieldNameObfuscator = $fieldNameObfuscator;
   }
 
   public function get($data = []) {
@@ -271,8 +276,7 @@ class Subscribers extends APIEndpoint {
   }
 
   private function deobfuscateFormPayload($data) {
-    $obfuscator = new FieldNameObfuscator();
-    return $obfuscator->deobfuscateFormPayload($data);
+    return $this->fieldNameObfuscator->deobfuscateFormPayload($data);
   }
 
   private function validateCaptcha($captchaSettings, $data) {
diff --git a/lib/Form/Util/FieldNameObfuscator.php b/lib/Form/Util/FieldNameObfuscator.php
index dc7bb1a750..9862b15cc6 100644
--- a/lib/Form/Util/FieldNameObfuscator.php
+++ b/lib/Form/Util/FieldNameObfuscator.php
@@ -9,9 +9,16 @@ class FieldNameObfuscator {
   const OBFUSCATED_FIELD_PREFIX = 'form_field_';
   const HASH_LENGTH = 12;
 
+  /** @var WPFunctions */
+  private $wp;
+
+  public function __construct(WPFunctions $wp) {
+    $this->wp = $wp;
+  }
+
   public function obfuscate($name) {
     $authKey = defined('AUTH_KEY') ? AUTH_KEY : '';
-    $hash = substr(md5($authKey . WPFunctions::get()->homeUrl() . $name), 0, self::HASH_LENGTH);
+    $hash = substr(md5($authKey . $this->wp->homeUrl() . $name), 0, self::HASH_LENGTH);
     return self::OBFUSCATED_FIELD_PREFIX . base64_encode($hash . '_' . $name);
   }
 
diff --git a/tests/integration/API/JSON/v1/SubscribersTest.php b/tests/integration/API/JSON/v1/SubscribersTest.php
index b8a8d71f41..984b76e3ce 100644
--- a/tests/integration/API/JSON/v1/SubscribersTest.php
+++ b/tests/integration/API/JSON/v1/SubscribersTest.php
@@ -60,6 +60,7 @@ class SubscribersTest extends \MailPoetTest {
     $settings = $container->get(SettingsController::class);
     $wp = $container->get(Functions::class);
     $this->captchaSession = new CaptchaSession($container->get(Functions::class));
+    $obfuscator = new FieldNameObfuscator($wp);
     $this->endpoint = new Subscribers(
       $container->get(BulkActionController::class),
       $container->get(SubscribersListings::class),
@@ -71,9 +72,9 @@ class SubscribersTest extends \MailPoetTest {
       $settings,
       $this->captchaSession,
       $container->get(ConfirmationEmailMailer::class),
-      new SubscriptionUrlFactory($wp, $settings, new LinkTokens)
+      new SubscriptionUrlFactory($wp, $settings, new LinkTokens),
+      $obfuscator
     );
-    $obfuscator = new FieldNameObfuscator();
     $this->obfuscatedEmail = $obfuscator->obfuscate('email');
     $this->obfuscatedSegments = $obfuscator->obfuscate('segments');
     $this->segment1 = Segment::createOrUpdate(['name' => 'Segment 1']);
diff --git a/tests/integration/Subscription/FormTest.php b/tests/integration/Subscription/FormTest.php
index 654a6a60c3..22295f484f 100644
--- a/tests/integration/Subscription/FormTest.php
+++ b/tests/integration/Subscription/FormTest.php
@@ -16,6 +16,7 @@ use MailPoet\Settings\SettingsRepository;
 use MailPoet\Subscription\Form;
 use MailPoet\Util\Security;
 use MailPoet\Util\Url as UrlHelper;
+use MailPoet\WP\Functions as WPFunctions;
 use MailPoetVendor\Idiorm\ORM;
 
 class FormTest extends \MailPoetTest {
@@ -55,7 +56,7 @@ class FormTest extends \MailPoetTest {
         ],
       ]
     );
-    $obfuscator = new FieldNameObfuscator();
+    $obfuscator = new FieldNameObfuscator(WPFunctions::get());
     $obfuscatedEmail = $obfuscator->obfuscate('email');
     $this->requestData = [
       'action' => 'mailpoet_subscription_form',
diff --git a/tests/unit/Form/Util/FieldNameObfuscatorTest.php b/tests/unit/Form/Util/FieldNameObfuscatorTest.php
index 4f79d500b7..dcdf1c255a 100644
--- a/tests/unit/Form/Util/FieldNameObfuscatorTest.php
+++ b/tests/unit/Form/Util/FieldNameObfuscatorTest.php
@@ -2,46 +2,43 @@
 
 namespace MailPoet\Form\Util;
 
-use Codeception\Stub;
 use MailPoet\WP\Functions as WPFunctions;
+use PHPUnit\Framework\MockObject\MockObject;
 
 class FieldNameObfuscatorTest extends \MailPoetUnitTest {
+
+  /** @var MockObject | WPFunctions */
+  private $wpMock;
+
+  /** @var FieldNameObfuscator */
+  private $obfuscator;
+
   public function _before() {
     parent::_before();
-    WPFunctions::set(
-      Stub::make(WPFunctions::class, [
-        'homeUrl' => 'http://example.com',
-      ])
-    );
+    $this->wpMock = $this->createMock(WPFunctions::class);
+    $this->wpMock->method('homeUrl')->willReturn('http://example.com');
+    $this->obfuscator = new FieldNameObfuscator($this->wpMock);
   }
 
   public function testObfuscateWorks() {
-    $obfuscator = new FieldNameObfuscator();
-    expect($obfuscator->obfuscate('email'))->notContains('email');
+    expect($this->obfuscator->obfuscate('email'))->notContains('email');
   }
 
   public function testObfuscateDeobfuscateWorks() {
-    $obfuscator = new FieldNameObfuscator();
-    $obfuscated = $obfuscator->obfuscate('email');
-    expect($obfuscator->deobfuscate($obfuscated))->equals('email');
+    $obfuscated = $this->obfuscator->obfuscate('email');
+    expect($this->obfuscator->deobfuscate($obfuscated))->equals('email');
   }
 
   public function testObfuscatePayloadWorks() {
-    $obfuscator = new FieldNameObfuscator();
-    $obfuscated = $obfuscator->obfuscate('email');
+    $obfuscated = $this->obfuscator->obfuscate('email');
     $data = [
       'regularField' => 'regularValue',
       $obfuscated => 'obfuscatedFieldValue',
     ];
-    $deobfuscatedPayload = $obfuscator->deobfuscateFormPayload($data);
+    $deobfuscatedPayload = $this->obfuscator->deobfuscateFormPayload($data);
     expect($deobfuscatedPayload)->equals([
       'regularField' => 'regularValue',
       'email' => 'obfuscatedFieldValue',
     ]);
   }
-
-  public function _after() {
-    parent::_after();
-    WPFunctions::set(new WPFunctions());
-  }
 }