diff --git a/lib/Config/PostEditorBlock.php b/lib/Config/PostEditorBlock.php
index 4612bb1466..ccb5a79d21 100644
--- a/lib/Config/PostEditorBlock.php
+++ b/lib/Config/PostEditorBlock.php
@@ -2,6 +2,7 @@
 
 namespace MailPoet\Config;
 
+use MailPoet\Entities\FormEntity;
 use MailPoet\Form\FormsRepository;
 use MailPoet\Form\Widget;
 use MailPoet\WP\Functions as WPFunctions;
@@ -72,7 +73,9 @@ class PostEditorBlock {
       $forms = $this->formsRepository->findAllNotDeleted();
       ?>
       <script type="text/javascript">
-        window.mailpoet_forms = <?php echo json_encode($forms) ?>;
+        window.mailpoet_forms = <?php echo json_encode(array_map(function(FormEntity $form) {
+          return $form->toArray();
+        }, $forms)) ?>;
         window.locale = {
           selectForm: '<?php echo __('Select a MailPoet form', 'mailpoet') ?>',
           createForm: '<?php echo __('Create a new form', 'mailpoet') ?>',
diff --git a/lib/Entities/FormEntity.php b/lib/Entities/FormEntity.php
index ea49c623a9..2f0cf3f68a 100644
--- a/lib/Entities/FormEntity.php
+++ b/lib/Entities/FormEntity.php
@@ -12,7 +12,7 @@ use MailPoetVendor\Doctrine\ORM\Mapping as ORM;
  * @ORM\Entity()
  * @ORM\Table(name="forms")
  */
-class FormEntity implements \JsonSerializable {
+class FormEntity {
   use AutoincrementedIdTrait;
   use CreatedAtTrait;
   use UpdatedAtTrait;
@@ -102,7 +102,7 @@ class FormEntity implements \JsonSerializable {
     $this->styles = $styles;
   }
 
-  public function jsonSerialize() {
+  public function toArray() {
     return [
       'id' => $this->getId(),
       'name' => $this->getName(),