diff --git a/build/build.js b/build/build.js
index 44edf874ff..2e7a027fb5 100644
--- a/build/build.js
+++ b/build/build.js
@@ -64,7 +64,7 @@ function processFile (inputLoc, out, replacements) {
           'transform-es2015-template-literals',
           'transform-es2015-shorthand-properties',
           'transform-es2015-for-of',
-          'transform-es2015-classes',
+          ['transform-es2015-classes', { loose: true }],
           'transform-es2015-destructuring',
           'transform-es2015-computed-properties',
           'transform-es2015-spread'
diff --git a/lib/internal/streams/BufferList.js b/lib/internal/streams/BufferList.js
index 8546bb06e4..d467615978 100644
--- a/lib/internal/streams/BufferList.js
+++ b/lib/internal/streams/BufferList.js
@@ -2,8 +2,6 @@
 
 /*<replacement>*/
 
-var _createClass = function () { function defineProperties(target, props) { for (var i = 0; i < props.length; i++) { var descriptor = props[i]; descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; if ("value" in descriptor) descriptor.writable = true; Object.defineProperty(target, descriptor.key, descriptor); } } return function (Constructor, protoProps, staticProps) { if (protoProps) defineProperties(Constructor.prototype, protoProps); if (staticProps) defineProperties(Constructor, staticProps); return Constructor; }; }();
-
 function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }
 
 var Buffer = require('safe-buffer').Buffer;
@@ -22,63 +20,55 @@ module.exports = function () {
     this.length = 0;
   }
 
-  _createClass(BufferList, [{
-    key: 'push',
-    value: function push(v) {
-      var entry = { data: v, next: null };
-      if (this.length > 0) this.tail.next = entry;else this.head = entry;
-      this.tail = entry;
-      ++this.length;
-    }
-  }, {
-    key: 'unshift',
-    value: function unshift(v) {
-      var entry = { data: v, next: this.head };
-      if (this.length === 0) this.tail = entry;
-      this.head = entry;
-      ++this.length;
-    }
-  }, {
-    key: 'shift',
-    value: function shift() {
-      if (this.length === 0) return;
-      var ret = this.head.data;
-      if (this.length === 1) this.head = this.tail = null;else this.head = this.head.next;
-      --this.length;
-      return ret;
-    }
-  }, {
-    key: 'clear',
-    value: function clear() {
-      this.head = this.tail = null;
-      this.length = 0;
-    }
-  }, {
-    key: 'join',
-    value: function join(s) {
-      if (this.length === 0) return '';
-      var p = this.head;
-      var ret = '' + p.data;
-      while (p = p.next) {
-        ret += s + p.data;
-      }return ret;
-    }
-  }, {
-    key: 'concat',
-    value: function concat(n) {
-      if (this.length === 0) return Buffer.alloc(0);
-      if (this.length === 1) return this.head.data;
-      var ret = Buffer.allocUnsafe(n >>> 0);
-      var p = this.head;
-      var i = 0;
-      while (p) {
-        copyBuffer(p.data, ret, i);
-        i += p.data.length;
-        p = p.next;
-      }
-      return ret;
+  BufferList.prototype.push = function push(v) {
+    var entry = { data: v, next: null };
+    if (this.length > 0) this.tail.next = entry;else this.head = entry;
+    this.tail = entry;
+    ++this.length;
+  };
+
+  BufferList.prototype.unshift = function unshift(v) {
+    var entry = { data: v, next: this.head };
+    if (this.length === 0) this.tail = entry;
+    this.head = entry;
+    ++this.length;
+  };
+
+  BufferList.prototype.shift = function shift() {
+    if (this.length === 0) return;
+    var ret = this.head.data;
+    if (this.length === 1) this.head = this.tail = null;else this.head = this.head.next;
+    --this.length;
+    return ret;
+  };
+
+  BufferList.prototype.clear = function clear() {
+    this.head = this.tail = null;
+    this.length = 0;
+  };
+
+  BufferList.prototype.join = function join(s) {
+    if (this.length === 0) return '';
+    var p = this.head;
+    var ret = '' + p.data;
+    while (p = p.next) {
+      ret += s + p.data;
+    }return ret;
+  };
+
+  BufferList.prototype.concat = function concat(n) {
+    if (this.length === 0) return Buffer.alloc(0);
+    if (this.length === 1) return this.head.data;
+    var ret = Buffer.allocUnsafe(n >>> 0);
+    var p = this.head;
+    var i = 0;
+    while (p) {
+      copyBuffer(p.data, ret, i);
+      i += p.data.length;
+      p = p.next;
     }
-  }]);
+    return ret;
+  };
 
   return BufferList;
 }();
\ No newline at end of file
diff --git a/test/parallel/test-stream-unpipe-event.js b/test/parallel/test-stream-unpipe-event.js
index 3eb8b28591..2f7ef2567b 100644
--- a/test/parallel/test-stream-unpipe-event.js
+++ b/test/parallel/test-stream-unpipe-event.js
@@ -1,5 +1,3 @@
-var _createClass = function () { function defineProperties(target, props) { for (var i = 0; i < props.length; i++) { var descriptor = props[i]; descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; if ("value" in descriptor) descriptor.writable = true; Object.defineProperty(target, descriptor.key, descriptor); } } return function (Constructor, protoProps, staticProps) { if (protoProps) defineProperties(Constructor.prototype, protoProps); if (staticProps) defineProperties(Constructor, staticProps); return Constructor; }; }();
-
 function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }
 
 function _possibleConstructorReturn(self, call) { if (!self) { throw new ReferenceError("this hasn't been initialised - super() hasn't been called"); } return call && (typeof call === "object" || typeof call === "function") ? call : self; }
@@ -25,15 +23,12 @@ var NullWriteable = function (_Writable) {
   function NullWriteable() {
     _classCallCheck(this, NullWriteable);
 
-    return _possibleConstructorReturn(this, (NullWriteable.__proto__ || Object.getPrototypeOf(NullWriteable)).apply(this, arguments));
+    return _possibleConstructorReturn(this, _Writable.apply(this, arguments));
   }
 
-  _createClass(NullWriteable, [{
-    key: '_write',
-    value: function _write(chunk, encoding, callback) {
-      return callback();
-    }
-  }]);
+  NullWriteable.prototype._write = function _write(chunk, encoding, callback) {
+    return callback();
+  };
 
   return NullWriteable;
 }(Writable);
@@ -44,15 +39,12 @@ var QuickEndReadable = function (_Readable) {
   function QuickEndReadable() {
     _classCallCheck(this, QuickEndReadable);
 
-    return _possibleConstructorReturn(this, (QuickEndReadable.__proto__ || Object.getPrototypeOf(QuickEndReadable)).apply(this, arguments));
+    return _possibleConstructorReturn(this, _Readable.apply(this, arguments));
   }
 
-  _createClass(QuickEndReadable, [{
-    key: '_read',
-    value: function _read() {
-      this.push(null);
-    }
-  }]);
+  QuickEndReadable.prototype._read = function _read() {
+    this.push(null);
+  };
 
   return QuickEndReadable;
 }(Readable);
@@ -63,13 +55,10 @@ var NeverEndReadable = function (_Readable2) {
   function NeverEndReadable() {
     _classCallCheck(this, NeverEndReadable);
 
-    return _possibleConstructorReturn(this, (NeverEndReadable.__proto__ || Object.getPrototypeOf(NeverEndReadable)).apply(this, arguments));
+    return _possibleConstructorReturn(this, _Readable2.apply(this, arguments));
   }
 
-  _createClass(NeverEndReadable, [{
-    key: '_read',
-    value: function _read() {}
-  }]);
+  NeverEndReadable.prototype._read = function _read() {};
 
   return NeverEndReadable;
 }(Readable);