diff --git a/mailpoet/lib/Cron/Workers/SendingQueue/SendingQueue.php b/mailpoet/lib/Cron/Workers/SendingQueue/SendingQueue.php
index e481d76525..19aa8d744b 100644
--- a/mailpoet/lib/Cron/Workers/SendingQueue/SendingQueue.php
+++ b/mailpoet/lib/Cron/Workers/SendingQueue/SendingQueue.php
@@ -30,7 +30,10 @@ use MailPoet\WP\Functions as WPFunctions;
 use MailPoetVendor\Carbon\Carbon;
 
 class SendingQueue {
+  /** @var MailerTask */
   public $mailerTask;
+
+  /** @var NewsletterTask  */
   public $newsletterTask;
 
   const TASK_TYPE = 'sending';
@@ -284,6 +287,10 @@ class SendingQueue {
         continue;
       }
 
+      if (!$newsletterEntity instanceof NewsletterEntity) {
+        continue;
+      }
+
       // render shortcodes and replace subscriber data in tracked links
       $preparedNewsletters[] =
         $this->newsletterTask->prepareNewsletterForSending(