diff --git a/ts/types/PhoneNumber.ts b/ts/types/PhoneNumber.ts
index fd9d9a3cc..1c6c2ff08 100644
--- a/ts/types/PhoneNumber.ts
+++ b/ts/types/PhoneNumber.ts
@@ -25,9 +25,7 @@ function _format(
 export const format = memoizee(_format, {
   primitive: true,
   // Convert the arguments to a unique string, required for primitive mode.
-  normalizer: function(args) {
-      return JSON.stringify(args);
-  }
+  normalizer: (...args) => JSON.stringify(args),
 });
 
 export function parse(