diff --git a/packages/core/object.js b/packages/core/object.js
index 393439b..e6a3ab9 100644
--- a/packages/core/object.js
+++ b/packages/core/object.js
@@ -3,7 +3,7 @@ export function map(O, fn) {
   const result = {};
   for (let i = 0; i < keys.length; i++) {
     const key = keys[i];
-    result[key] = fn(O[key]);
+    result[key] = fn(O[key], key);
   }
   return result;
 }