diff --git a/packages/flutter/lib/src/widgets/overlay.dart b/packages/flutter/lib/src/widgets/overlay.dart
index d3d4fe1992e..7e692e25fc0 100644
--- a/packages/flutter/lib/src/widgets/overlay.dart
+++ b/packages/flutter/lib/src/widgets/overlay.dart
@@ -519,7 +519,7 @@ class _TheatreElement extends RenderObjectElement {
 // children of its primary subtree's stack can be moved to this object's list
 // of zombie children without changing their parent data objects.
 class _RenderTheatre extends RenderBox
-  with RenderObjectWithChildMixin<RenderStack>, RenderProxyBoxMixin<RenderBox>,
+  with RenderObjectWithChildMixin<RenderStack>, RenderProxyBoxMixin<RenderStack>,
        ContainerRenderObjectMixin<RenderBox, StackParentData> {
 
   @override