diff --git a/typescript/types/layout.d.ts b/typescript/types/layout.d.ts
index 4329d0831..e15d86b64 100644
--- a/typescript/types/layout.d.ts
+++ b/typescript/types/layout.d.ts
@@ -153,6 +153,6 @@ declare module Layout {
       r?: Rotation,
     } | {
       type: "custom",
-      render: (h: RenderedHierarchy) => void,
+      render: (this: RenderedHierarchy, h: RenderedHierarchy) => void,
     };
 }