diff --git a/index.d.ts b/index.d.ts
index c079e2c..1f51271 100644
--- a/index.d.ts
+++ b/index.d.ts
@@ -22,7 +22,7 @@ declare namespace directoryTree {
     children?: DirectoryTree<C>[];
     extension?: string;
     isSymbolicLink?: boolean;
-    custom: C;
+    custom?: C;
   }
 
   export interface DirectoryTreeOptions {