diff --git a/js/components/ResizeTarget.tsx b/js/components/ResizeTarget.tsx
index 2ae7a22e..6c6f61f3 100644
--- a/js/components/ResizeTarget.tsx
+++ b/js/components/ResizeTarget.tsx
@@ -9,7 +9,8 @@ type Size = [number, number];
 interface Props {
   currentSize: Size;
   setWindowSize(size: Size): void;
-  widthOnly: boolean;
+  widthOnly?: boolean;
+  id?: string;
 }
 
 export default class ResizeTarget extends React.Component<Props> {