diff --git a/src/index.js b/src/index.js
index 379073e..10e0d8b 100644
--- a/src/index.js
+++ b/src/index.js
@@ -4,7 +4,7 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
+ * @flow strict
  */
 
 // A Function, which when given an Array of keys, returns a Promise of an Array