diff --git a/lib/merkleTree.js b/lib/merkleTree.js
index 097b4806..8c580652 100644
--- a/lib/merkleTree.js
+++ b/lib/merkleTree.js
@@ -1,58 +1,48 @@
-/*
-
-Ported from https://github.com/slush0/stratum-mining/blob/master/lib/merkletree.py
-
- */
-
 var util = require('./util.js');
 
 var MerkleTree = module.exports = function MerkleTree(data){
+    this.data = data.filter(element => element != null);
+    this.steps = calculateSteps(this.data);
+};
 
-    function merkleJoin(h1, h2){
-        var joined = Buffer.concat([h1, h2]);
-        var dhashed = util.sha256d(joined);
-        return dhashed;
+function merkleJoin(h1, h2){
+    if (h1 === null || h2 === null) {
+        throw new Error('Merkle join received null input');
     }
+    var joined = Buffer.concat([h1, h2]);
+    var dhashed = util.sha256d(joined);
+    return dhashed;
+}
 
-    function calculateSteps(data){
-        var L = data;
-        var steps = [];
-        var PreL = [null];
-        var StartL = 2;
-        var Ll = L.length;
-
-        if (Ll > 1){
-            while (true){
+function calculateSteps(data){
+    var L = data;
+    var steps = [];
+    var Ll = L.length;
 
-                if (Ll === 1)
-                    break;
+    if (Ll > 1){
+        while (true){
+            if (Ll === 1) break;
 
-                steps.push(L[1]);
+            steps.push(L[1]);
 
-                if (Ll % 2)
-                    L.push(L[L.length - 1]);
+            if (Ll % 2) L.push(L[L.length - 1]);
 
-                var Ld = [];
-                var r = util.range(StartL, Ll, 2);
-                r.forEach(function(i){
+            var Ld = [];
+            for (var i = 0; i < L.length; i += 2) {
+                if (i + 1 < L.length) {
                     Ld.push(merkleJoin(L[i], L[i + 1]));
-                });
-                L = PreL.concat(Ld);
-                Ll = L.length;
+                }
             }
+            L = Ld;
+            Ll = L.length;
         }
-       return steps;
     }
-
-    this.data = data;
-    this.steps = calculateSteps(data);
-
+    return steps;
 }
-MerkleTree.prototype = {
-    withFirst: function(f){
-        this.steps.forEach(function(s){
-            f = util.sha256d(Buffer.concat([f, s]));
-        });
-        return f;
-    }
-};
\ No newline at end of file
+
+MerkleTree.prototype.withFirst = function(f){
+    this.steps.forEach(function(s){
+        f = util.sha256d(Buffer.concat([f, s]));
+    });
+    return f;
+};