diff --git a/lib/Models/SendingQueue.php b/lib/Models/SendingQueue.php
index ba792793ab..1edcdfa4e1 100644
--- a/lib/Models/SendingQueue.php
+++ b/lib/Models/SendingQueue.php
@@ -73,13 +73,13 @@ class SendingQueue extends Model {
     if (!Helpers::isJson($this->newsletterRenderedBody) && !is_null($this->newsletterRenderedBody)) {
       $this->set(
         'newsletter_rendered_body',
-        json_encode($this->newsletterRenderedBody)
+        (string)json_encode($this->newsletterRenderedBody)
       );
     }
     if (!is_null($this->meta) && !Helpers::isJson($this->meta)) {
       $this->set(
         'meta',
-        json_encode($this->meta)
+        (string)json_encode($this->meta)
       );
     }
     parent::save();