diff --git a/plugins/ActivityPub/Util/Model/Activity.php b/plugins/ActivityPub/Util/Model/Activity.php
index 200e96dbe2..32eb8c95d4 100644
--- a/plugins/ActivityPub/Util/Model/Activity.php
+++ b/plugins/ActivityPub/Util/Model/Activity.php
@@ -194,7 +194,9 @@ class Activity extends Model
             }
         }
 
-        $attr['object']->set('@context', null);
+        if (!\is_string($attr['object'])) {
+            $attr['object']->set('@context', null);
+        }
         $type = self::jsonToType($attr);
         Event::handle('ActivityPubAddActivityStreamsTwoData', [$type->get('type'), &$type]);
         return $type->toJson($options);