diff --git a/lib/6to5/generation/generator.js b/lib/6to5/generation/generator.js
index 7f2ce983de..4406a84f46 100644
--- a/lib/6to5/generation/generator.js
+++ b/lib/6to5/generation/generator.js
@@ -57,6 +57,7 @@ CodeGenerator.generators = {
   methods:          require("./generators/methods"),
   modules:          require("./generators/modules"),
   types:            require("./generators/types"),
+  flow:             require("./generators/flow"),
   base:             require("./generators/base"),
   jsx:              require("./generators/jsx")
 };
diff --git a/lib/6to5/generation/generators/flow.js b/lib/6to5/generation/generators/flow.js
new file mode 100644
index 0000000000..f96e45bde0
--- /dev/null
+++ b/lib/6to5/generation/generators/flow.js
@@ -0,0 +1,3 @@
+exports.ClassProperty = function () {
+  throw new Error("not implemented");
+};
diff --git a/lib/6to5/generation/generators/statements.js b/lib/6to5/generation/generators/statements.js
index f96ecb29fa..c6c471b638 100644
--- a/lib/6to5/generation/generators/statements.js
+++ b/lib/6to5/generation/generators/statements.js
@@ -164,6 +164,12 @@ exports.VariableDeclaration = function (node, print, parent) {
   }
 };
 
+exports.PrivateDeclaration = function (node, print) {
+  this.push("private ");
+  print.join(node.declarations, { separator: ", " });
+  this.semicolon();
+};
+
 exports.VariableDeclarator = function (node, print) {
   if (node.init) {
     print(node.id);
diff --git a/lib/6to5/patch.js b/lib/6to5/patch.js
index b50b96718a..f846fdf2f0 100644
--- a/lib/6to5/patch.js
+++ b/lib/6to5/patch.js
@@ -30,6 +30,11 @@ def("VirtualPropertyExpression")
   .field("object", def("Expression"))
   .field("property", or(def("Identifier"), def("Expression")));
 
+def("PrivateDeclaration")
+  .bases("Declaration")
+  .build("declarations")
+  .field("declarations", [def("Identifier")]);
+
 // Playground
 def("BindMemberExpression")
   .bases("Expression")
diff --git a/lib/6to5/transformation/transformers/es6-classes.js b/lib/6to5/transformation/transformers/es6-classes.js
index 98ac4d59d6..9292aba0ea 100644
--- a/lib/6to5/transformation/transformers/es6-classes.js
+++ b/lib/6to5/transformation/transformers/es6-classes.js
@@ -4,11 +4,11 @@ var t        = require("../../types");
 var _        = require("lodash");
 
 exports.ClassDeclaration = function (node, parent, file, scope) {
-  return new Class(node, file, scope, true).run();
+  return new Class(node, file, scope, false).run();
 };
 
 exports.ClassExpression = function (node, parent, file, scope) {
-  return new Class(node, file, scope, false).run();
+  return new Class(node, file, scope, true).run();
 };
 
 /**
@@ -17,14 +17,14 @@ exports.ClassExpression = function (node, parent, file, scope) {
  * @param {Node} node
  * @param {File} file
  * @param {Scope} scope
- * @param {Boolean} isStatement
+ * @param {Boolean} closure
  */
 
-function Class(node, file, scope, isStatement) {
-  this.isStatement = isStatement;
-  this.scope       = scope;
-  this.node        = node;
-  this.file        = file;
+function Class(node, file, scope, closure) {
+  this.closure = closure;
+  this.scope   = scope;
+  this.node    = node;
+  this.file    = file;
 
   this.instanceMutatorMap = {};
   this.staticMutatorMap   = {};
@@ -80,9 +80,7 @@ Class.prototype.run = function () {
 
   this.buildBody();
 
-  if (this.isStatement) {
-    return body;
-  } else {
+  if (this.closure) {
     if (body.length === 1) {
       // only a constructor so no need for a closure container
       return constructor;
@@ -93,6 +91,8 @@ Class.prototype.run = function () {
         []
       );
     }
+  } else {
+    return body;
   }
 };
 
@@ -109,12 +109,17 @@ Class.prototype.buildBody = function () {
   var self        = this;
 
   _.each(classBody, function (node) {
-    self.replaceInstanceSuperReferences(node);
+    if (t.isMethodDefinition(node)) {
+      self.replaceInstanceSuperReferences(node);
 
-    if (node.key.name === "constructor") {
-      self.pushConstructor(node);
-    } else {
-      self.pushMethod(node);
+      if (node.key.name === "constructor") {
+        self.pushConstructor(node);
+      } else {
+        self.pushMethod(node);
+      }
+    } else if (t.isPrivateDeclaration(node)) {
+      self.closure = true;
+      body.unshift(node);
     }
   });
 
diff --git a/lib/6to5/transformation/transformers/es7-abstract-references.js b/lib/6to5/transformation/transformers/es7-abstract-references.js
index 266aa9d09b..73d86adb7f 100644
--- a/lib/6to5/transformation/transformers/es7-abstract-references.js
+++ b/lib/6to5/transformation/transformers/es7-abstract-references.js
@@ -96,3 +96,9 @@ exports.VirtualPropertyExpression = function (node) {
     OBJECT:   node.object
   });
 };
+
+exports.PrivateDeclaration = function (node) {
+  return t.variableDeclaration("const", node.declarations.map(function (id) {
+    return t.variableDeclarator(id, t.newExpression(t.identifier("WeakMap"), []));
+  }));
+};
diff --git a/lib/6to5/types/visitor-keys.json b/lib/6to5/types/visitor-keys.json
index fc78a716e5..b90e63942f 100644
--- a/lib/6to5/types/visitor-keys.json
+++ b/lib/6to5/types/visitor-keys.json
@@ -5,6 +5,7 @@
   "AssignmentExpression":      ["left", "right"],
   "AwaitExpression":           ["argument"],
   "BinaryExpression":          ["left", "right"],
+  "BindFunctionExpression":    ["callee", "arguments"],
   "BindMemberExpression":      ["object", "property", "arguments"],
   "BlockStatement":            ["body"],
   "BreakStatement":            ["label"],
@@ -13,6 +14,7 @@
   "ClassBody":                 ["body"],
   "ClassDeclaration":          ["id", "body", "superClass"],
   "ClassExpression":           ["id", "body", "superClass"],
+  "ClassProperty":             ["key"],
   "ComprehensionBlock":        ["left", "right", "body"],
   "ComprehensionExpression":   ["filter", "blocks", "body"],
   "ConditionalExpression":     ["test", "consequent", "alternate"],
@@ -44,7 +46,7 @@
   "ObjectExpression":          ["properties"],
   "ObjectPattern":             ["properties"],
   "ParenthesizedExpression":   ["expression"],
-  "BindFunctionExpression":    ["callee", "arguments"],
+  "PrivateDeclaration":        ["declarations"],
   "Program":                   ["body"],
   "Property":                  ["key", "value"],
   "ReturnStatement":           ["argument"],
diff --git a/test/fixtures/generation/types/PrivateDeclaration/actual.js b/test/fixtures/generation/types/PrivateDeclaration/actual.js
new file mode 100644
index 0000000000..c9c6b03ef6
--- /dev/null
+++ b/test/fixtures/generation/types/PrivateDeclaration/actual.js
@@ -0,0 +1,7 @@
+private A;
+private B, C;
+
+class Test {
+  private A;
+  private B, C;
+}
diff --git a/test/fixtures/generation/types/PrivateDeclaration/expected.js b/test/fixtures/generation/types/PrivateDeclaration/expected.js
new file mode 100644
index 0000000000..c9c6b03ef6
--- /dev/null
+++ b/test/fixtures/generation/types/PrivateDeclaration/expected.js
@@ -0,0 +1,7 @@
+private A;
+private B, C;
+
+class Test {
+  private A;
+  private B, C;
+}
diff --git a/test/fixtures/transformation/es7-abstract-references/private/actual.js b/test/fixtures/transformation/es7-abstract-references/private/actual.js
new file mode 100644
index 0000000000..9643ff19c2
--- /dev/null
+++ b/test/fixtures/transformation/es7-abstract-references/private/actual.js
@@ -0,0 +1,12 @@
+private A;
+private B, C;
+
+class D {
+  private E;
+  private F, G;
+}
+
+var H = class {
+  private I;
+  private J, K;
+};
diff --git a/test/fixtures/transformation/es7-abstract-references/private/expected.js b/test/fixtures/transformation/es7-abstract-references/private/expected.js
new file mode 100644
index 0000000000..91d4b390d1
--- /dev/null
+++ b/test/fixtures/transformation/es7-abstract-references/private/expected.js
@@ -0,0 +1,19 @@
+"use strict";
+
+var A = new WeakMap();
+var B = new WeakMap(), C = new WeakMap();
+(function () {
+  var F = new WeakMap(), G = new WeakMap();
+  var E = new WeakMap();
+  var D = function D() {};
+
+  return D;
+})()
+
+var H = (function () {
+  var J = new WeakMap(), K = new WeakMap();
+  var I = new WeakMap();
+  var _class = function () {};
+
+  return _class;
+})();