diff --git a/src/PersistentData/PersistentDataManager.php b/src/PersistentData/PersistentDataManager.php
index 60fec89..e3096d2 100644
--- a/src/PersistentData/PersistentDataManager.php
+++ b/src/PersistentData/PersistentDataManager.php
@@ -125,7 +125,8 @@ class PersistentDataManager implements IPersistentDataManager
             }
         } else {
             if ($model instanceof ModelWithSlug) {
-                $modified['slug'] = $this->generateUniqueSlug($model, $modified['slug']);
+                $slug = $model->generateSlug();
+                $modified['slug'] = $this->generateUniqueSlug($model, $slug);
             }
 
             $modify->fill($modified);