diff --git a/src/index.js b/src/index.js
index 4950746ff..c1614deb6 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,3 +1,4 @@
+// @flow
 // Copyright (c) 2015 Uber Technologies, Inc.
 
 // Permission is hereby granted, free of charge, to any person obtaining a copy