diff --git a/controller/upload_file.rst b/controller/upload_file.rst
index 18d0fee4be8..b2360426785 100644
--- a/controller/upload_file.rst
+++ b/controller/upload_file.rst
@@ -255,7 +255,7 @@ logic to a separate service::
         public function upload(UploadedFile $file)
         {
             $originalFilename = pathinfo($file->getClientOriginalName(), PATHINFO_FILENAME);
-            $safeFilename = $slugger->slug($originalFilename);
+            $safeFilename = $this->slugger->slug($originalFilename);
             $fileName = $safeFilename.'-'.uniqid().'.'.$file->guessExtension();
 
             try {