diff --git a/lib/ui/compositing.dart b/lib/ui/compositing.dart
index d29e5f1a8e57dbc68a7ed25631e746ba883239b7..1bf7b1fd60a3859ab726d5f786004f99c349faa1 100644
--- a/lib/ui/compositing.dart
+++ b/lib/ui/compositing.dart
@@ -37,7 +37,7 @@ class Scene extends NativeFieldWrapperClass2 {
     );
   }
 
-  String _toImage(int width, int height, _Callback<_Image> callback) native 'Scene_toImage';
+  String? _toImage(int width, int height, _Callback<_Image> callback) native 'Scene_toImage';
 
   /// Releases the resources used by this scene.
   ///