diff --git a/lib/Cron/Workers/StatsNotifications/Worker.php b/lib/Cron/Workers/StatsNotifications/Worker.php
index a5e92b99d9..37afdf9e9c 100644
--- a/lib/Cron/Workers/StatsNotifications/Worker.php
+++ b/lib/Cron/Workers/StatsNotifications/Worker.php
@@ -100,7 +100,11 @@ class Worker {
           throw $e;
         }
       } finally {
-        $this->markTaskAsFinished($statsNotificationEntity->getTask());
+        $task = $statsNotificationEntity->getTask();
+        if ($task instanceof ScheduledTask) {
+          $this->markTaskAsFinished($task);
+        }
+
       }
       $this->cronHelper->enforceExecutionLimit($timer);
     }
@@ -108,6 +112,9 @@ class Worker {
 
   private function constructNewsletter(StatsNotificationEntity $statsNotificationEntity) {
     $newsletter = $statsNotificationEntity->getNewsletter();
+    if (!$newsletter instanceof NewsletterEntity) {
+      throw new \RuntimeException('Missing newsletter entity for statistic notification.');
+    }
     $link = $this->newsletterLinkRepository->findTopLinkForNewsletter((int)$newsletter->getId());
     $context = $this->prepareContext($newsletter, $link);
     $subject = $newsletter->getLatestQueue()->getNewsletterRenderedSubject();
diff --git a/lib/Entities/StatsNotificationEntity.php b/lib/Entities/StatsNotificationEntity.php
index 673ed9a4f6..35728ebc0d 100644
--- a/lib/Entities/StatsNotificationEntity.php
+++ b/lib/Entities/StatsNotificationEntity.php
@@ -20,13 +20,13 @@ class StatsNotificationEntity {
 
   /**
    * @ORM\OneToOne(targetEntity="MailPoet\Entities\NewsletterEntity")
-   * @var NewsletterEntity
+   * @var NewsletterEntity|null
    */
   private $newsletter;
 
   /**
    * @ORM\OneToOne(targetEntity="MailPoet\Entities\ScheduledTaskEntity")
-   * @var ScheduledTaskEntity
+   * @var ScheduledTaskEntity|null
    */
   private $task;
 
@@ -36,7 +36,7 @@ class StatsNotificationEntity {
   }
 
   /**
-   * @return NewsletterEntity
+   * @return NewsletterEntity|null
    */
   public function getNewsletter() {
     $this->safelyLoadToOneAssociation('newsletter');
@@ -44,7 +44,7 @@ class StatsNotificationEntity {
   }
 
   /**
-   * @return ScheduledTaskEntity
+   * @return ScheduledTaskEntity|null
    */
   public function getTask() {
     $this->safelyLoadToOneAssociation('task');