diff --git a/src/merge-sort.js b/src/merge-sort.js
index 3ed2758..88d6cb5 100644
--- a/src/merge-sort.js
+++ b/src/merge-sort.js
@@ -2,31 +2,39 @@
  * Sorts an array of integers using the MergeSort algorithm.
  * @param {Array.<number>} items Array of items to be sorted.
  */
-aij.mergeSort = function(items) {
-    var merge = function(left, right) {
-        var result = [];
+aij.mergeSort = (function () {
+  "use strict";
 
-        while (left.length || right.length) {
-            result.push(
-                left.length && left[0] <= (right[0] || Number.MAX_VALUE) ?
-                left.shift() :
-                right.shift());
-        }
-
-        return result;
+  function simpleMerge(a, from, pivot, to, buffer) {
+    var i = -1;
+    while (++i < to - pivot) {
+      buffer[i] = a[i + pivot];
     }
+    --i;
+    --pivot;
+    while (i >= 0) {
+      --to;
+      if (pivot >= from && buffer[i] < a[pivot]) {
+        a[to] = a[pivot];
+        --pivot;
+      } else {
+        a[to] = buffer[i];
+        --i;
+      }
+    }
+  }
 
-    var sort = function(arr) {
-        var middle = arr && (arr.length / 2) << 0;
-
-        if (!middle) {
-            return arr;
-        } else if (arr.length === 2) {
-            return arr[1] < arr[0] ? arr.reverse() : arr;
-        }
-
-        return merge(sort(arr.slice(0, middle)), sort(arr.slice(middle)));
+  function mergeSort(a, from, to, buffer) {
+    if (to - from > 1) {
+      var middle = from + Math.floor((to - from) / 2);
+      mergeSort(a, from, middle, buffer);
+      mergeSort(a, middle, to, buffer);
+      simpleMerge(a, from, middle, to, buffer);
     }
+    return a;
+  }
 
-    return sort(items);
-};
+  return function (items) {
+    return mergeSort(items, 0, items.length, items.slice(0));
+  };
+}());