diff --git a/lib/6to5/generation/buffer.js b/lib/6to5/generation/buffer.js
index e40d4787f7..1ba135089f 100644
--- a/lib/6to5/generation/buffer.js
+++ b/lib/6to5/generation/buffer.js
@@ -61,7 +61,7 @@ Buffer.prototype.space = function () {
 Buffer.prototype.removeLast = function (cha) {
   if (!this.isLast(cha)) return;
 
-  this.buf = this.buf.slice(0, -1);
+  this.buf = this.buf.substr(0, this.buf.length - 1);
   this.position.unshift(cha);
 };
 
@@ -114,13 +114,14 @@ Buffer.prototype._push = function (str) {
 };
 
 Buffer.prototype.endsWith = function (str) {
-  return this.buf.slice(-str.length) === str;
+  var d = this.buf.length - str.length;
+  return d >= 0 && this.buf.lastIndexOf(str) === d;
 };
 
 Buffer.prototype.isLast = function (cha, trimRight) {
   var buf = this.buf;
   if (trimRight) buf = util.trimRight(buf);
-  var last = _.last(buf);
+  var last = buf[buf.length - 1];
 
   if (_.isArray(cha)) {
     return _.contains(cha, last);
diff --git a/lib/6to5/generation/node/index.js b/lib/6to5/generation/node/index.js
index 8828ba9030..42daaafaec 100644
--- a/lib/6to5/generation/node/index.js
+++ b/lib/6to5/generation/node/index.js
@@ -6,14 +6,19 @@ var t          = require("../../types");
 var _          = require("lodash");
 
 var find = function (obj, node, parent) {
+  if (!obj) return;
   var result;
 
-  _.each(obj, function (fn, type) {
+  var types = Object.keys(obj);
+  for (var i = 0; i < types.length; i++) {
+    var type = types[i];
+
     if (t["is" + type](node)) {
+      var fn = obj[type];
       result = fn(node, parent);
-      if (result != null) return false;
+      if (result != null) break;
     }
-  });
+  }
 
   return result;
 };
@@ -99,7 +104,13 @@ _.each(Node.prototype, function (fn, key) {
   Node[key] = function (node, parent) {
     var n = new Node(node, parent);
 
-    var args = _.toArray(arguments).slice(2);
+    // Avoid leaking arguments to prevent deoptimization
+    var skipCount = 2;
+    var args = new Array(arguments.length - skipCount);
+    for (var i = 0; i < args.length; i++) {
+      args[i] = arguments[i + 2];
+    }
+
     return n[key].apply(n, args);
   };
 });