diff --git a/landing/button.react.js b/landing/button.react.js
--- a/landing/button.react.js
+++ b/landing/button.react.js
@@ -5,7 +5,7 @@
 import css from './button.css';
 
 type Props = {
-  +onClick: (e: Event) => Promise<void>,
+  +onClick: (event: SyntheticEvent<HTMLButtonElement>) => mixed,
   +children?: React.Node,
 };