diff --git a/lib/Service/NotesService.php b/lib/Service/NotesService.php
index 644b61f0c..d191f8c53 100644
--- a/lib/Service/NotesService.php
+++ b/lib/Service/NotesService.php
@@ -310,7 +310,9 @@ public function getAttachment(string $userId, int $noteid, string $path) : File
 			}
 		}
 		$targetNode = $notesFolder->get(implode('/', $p));
-		assert($targetNode instanceof \OCP\Files\File);
+		if (!($targetNode instanceof File)) {
+			throw new NoteDoesNotExistException();
+		}
 		return $targetNode;
 	}