diff --git a/problems/implement_map_with_reduce/solution.js b/problems/implement_map_with_reduce/solution.js
index 1e3f5d3..4c9ca8a 100644
--- a/problems/implement_map_with_reduce/solution.js
+++ b/problems/implement_map_with_reduce/solution.js
@@ -1,5 +1,5 @@
-module.exports = function map(arr, fn) {
+module.exports = function map(arr, fn, thisArg) {
   return arr.reduce(function(acc, item, index, arr) {
-    return acc.concat(fn(item, index, arr))
+    return acc.concat(fn.call(thisArg, item, index, arr))
   }, [])
 }