diff --git a/src/Generators/stubs/datatables.stub b/src/Generators/stubs/datatables.stub
index 59a118a..03ff64c 100644
--- a/src/Generators/stubs/datatables.stub
+++ b/src/Generators/stubs/datatables.stub
@@ -75,7 +75,7 @@ class DummyClass extends DataTable
      *
      * @return string
      */
-    protected function filename()
+    protected function filename() : string
     {
         return 'DummyFilename_' . date('YmdHis');
     }