diff --git a/CHANGELOG.md b/CHANGELOG.md
index 021437a771..9d2e5af03e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 1.12.27
+
+ * Put experimental ES7 features behind a flag `--experimental` and `experimental` option.
+
 # 1.12.26
 
  * Support computed property destructuring.
diff --git a/bin/6to5/index.js b/bin/6to5/index.js
index 9f41d92530..d79fe08162 100755
--- a/bin/6to5/index.js
+++ b/bin/6to5/index.js
@@ -11,6 +11,7 @@ commander.option("-s, --source-maps", "Save source map alongside the compiled co
 commander.option("-f, --filename [filename]", "Filename to use when reading from stdin - this will be used in source-maps, errors etc [stdin]", "stdin");
 commander.option("-w, --watch", "Recompile files on changes");
 commander.option("-r, --runtime", "Replace 6to5 declarations with references to a runtime");
+commander.option("-e, --experimental", "Enable experimental support for proposed ES7 features");
 
 commander.option("-m, --modules [modules]", "Module formatter type to use [common]", "common");
 commander.option("-w, --whitelist [whitelist]", "Whitelist of transformers to ONLY use", util.list);
@@ -87,11 +88,12 @@ if (errors.length) {
 
 exports.opts = {
   sourceMapName: commander.outFile,
+  amdModuleIds:  commander.amdModuleIds,
+  experimental:  commander.experimental,
   blacklist:     commander.blacklist,
   whitelist:     commander.whitelist,
   sourceMap:     commander.sourceMaps || commander.sourceMapsInline,
   comments:      !commander.removeComments,
-  amdModuleIds:   commander.amdModuleIds,
   runtime:       commander.runtime,
   modules:       commander.modules
 };
diff --git a/bin/_6to5-node b/bin/_6to5-node
index 89faa4364b..c9fe95968f 100644
--- a/bin/_6to5-node
+++ b/bin/_6to5-node
@@ -8,10 +8,11 @@ var util      = require("../lib/6to5/util");
 var vm        = require("vm");
 var _         = require("lodash");
 
-commander.option("-e, --eval [script]", "evaluate script");
-commander.option("-p, --print", "evaluate script and print result");
-commander.option("-i, --ignore [regex]", "ignore all files that match this regex when using the require hook");
-commander.option("-x, --extensions [extensions]", "list of extensions to hook into [.es6,.js]", util.list);
+commander.option("-e, --eval [script]", "Evaluate script");
+commander.option("-p, --print", "Evaluate script and print result");
+commander.option("-i, --ignore [regex]", "Ignore all files that match this regex when using the require hook");
+commander.option("-x, --extensions [extensions]", "List of extensions to hook into [.es6,.js]");
+commander.option("-r, --experimental", "Enable experimental support for proposed ES7 features");
 
 var pkg = require("../package.json");
 commander.version(pkg.version);
@@ -20,17 +21,11 @@ commander.parse(process.argv);
 
 //
 
-var registerOpts = {};
-
-if (commander.ignore) {
-  registerOpts.ignoreRegex = new RegExp(commander.ignore);
-}
-
-if (commander.extensions && commander.extensions.length) {
-  registerOpts.extensions = commander.extensions;
-}
-
-to5.register(registerOpts);
+to5.register({
+  experimental: commander.experimental,
+  extensions:   commander.extensions,
+  ignore:       commander.ignore
+});
 
 //
 
diff --git a/doc/features.md b/doc/features.md
index 78978ae250..1d2732533d 100644
--- a/doc/features.md
+++ b/doc/features.md
@@ -1,6 +1,6 @@
 # Features
 
-## Array comprehension
+## Array comprehension ([experimental](usage.md#experimental))
 
 ```javascript
 var results = [for (c of customers) if (c.city == "Seattle") { name: c.name, age: c.age }]
@@ -31,7 +31,7 @@ var bob = {
 };
 ```
 
-## Async functions
+## Async functions ([experimental](usage.md#experimental))
 
 ```javascript
 async function chainAnimationsAsync(elem, animations) {
@@ -150,7 +150,7 @@ for (var n of fibonacci()) {
 }
 ```
 
-## Generator comprehension
+## Generator comprehension ([experimental](usage.md#experimental))
 
 ```javascript
 var nums = [1, 2, 3, 4, 5, 6];
diff --git a/doc/index.md b/doc/index.md
index b61957bc27..005d513b42 100644
--- a/doc/index.md
+++ b/doc/index.md
@@ -31,8 +31,8 @@ And it doesn't end here! To see all the ways you can use 6to5, check out the
 
 ## [Features](features.md)
 
- - [Array comprehension](features.md#array-comprehension)
- - [Async functions](features.md#async-functions)
+ - [Array comprehension](features.md#array-comprehension) ([experimental](usage.md#experimental))
+ - [Async functions](features.md#async-functions) ([experimental](usage.md#experimental))
  - [Arrow functions](features.md#arrow-functions)
  - [Classes](features.md#classes)
  - [Computed property names](features.md#computed-property-names)
@@ -41,7 +41,7 @@ And it doesn't end here! To see all the ways you can use 6to5, check out the
  - [Destructuring](features.md#destructuring)
  - [For-of](features.md#for-of)
  - [Generators](features.md#generators)
- - [Generator comprehension](features.md#generator-comprehension)
+ - [Generator comprehension](features.md#generator-comprehension) ([experimental](usage.md#experimental))
  - [Let scoping](features.md#let-scoping)
  - [Modules](features.md#modules)
  - [Numeric literals](features.md#numeric-literals)
diff --git a/doc/usage.md b/doc/usage.md
index ce51614591..1e4a75db47 100644
--- a/doc/usage.md
+++ b/doc/usage.md
@@ -135,7 +135,11 @@ to5.transformFile("filename.js", options, function (err, result) {
 
   // Output comments in generated output
   // Default: true
-  comments: false
+  comments: false,
+
+  // Enable support for experimental ES7 features
+  // Default: false
+  experimental: true
 }
 ```
 
@@ -181,3 +185,9 @@ require("6to5/register")({
   extensions: [".js", ".es6"]
 });
 ```
+
+## Experimental
+
+6to5 also has experimental support for ES7 proposals. You can enable this with
+the `experimental: true` option when using the [Node API](#node) or
+`--experimental` when using the [CLI](#cli).
diff --git a/lib/6to5/file.js b/lib/6to5/file.js
index ed343d9298..0e043292c5 100644
--- a/lib/6to5/file.js
+++ b/lib/6to5/file.js
@@ -25,15 +25,16 @@ File.normaliseOptions = function (opts) {
   opts = _.cloneDeep(opts || {});
 
   _.defaults(opts, {
-    whitespace: true,
-    blacklist:  [],
-    whitelist:  [],
-    sourceMap:  false,
-    comments:   true,
-    filename:   "unknown",
-    modules:    "common",
-    runtime:    false,
-    code:       true
+    experimental: false,
+    whitespace:   true,
+    blacklist:    [],
+    whitelist:    [],
+    sourceMap:    false,
+    comments:     true,
+    filename:     "unknown",
+    modules:      "common",
+    runtime:      false,
+    code:         true
   });
 
   // normalise windows path separators to unix
diff --git a/lib/6to5/register.js b/lib/6to5/register.js
index 30fc5e5a82..86035276b5 100644
--- a/lib/6to5/register.js
+++ b/lib/6to5/register.js
@@ -57,24 +57,25 @@ blacklistTest("unicodeRegex", function () { new RegExp("foo", "u"); });
 
 //
 
-var ignoreRegex = /node_modules/;
+var transformOpts = {};
+var ignoreRegex   = /node_modules/;
 var onlyRegex;
-var whitelist   = [];
-var exts        = {};
-var maps        = {};
-var old         = require.extensions[".js"];
+var whitelist     = [];
+var exts          = {};
+var maps          = {};
+var old           = require.extensions[".js"];
 
 var loader = function (m, filename) {
   if ((ignoreRegex && ignoreRegex.test(filename)) || (onlyRegex && !onlyRegex.test(filename))) {
     return old.apply(this, arguments);
   }
 
-  var result = to5.transformFileSync(filename, {
+  var result = to5.transformFileSync(filename, _.extend({
     whitelist: whitelist,
     blacklist: blacklist,
     sourceMap: true,
     modules:   "commonInterop"
-  });
+  }, transformOpts));
 
   maps[filename] = result.map;
 
@@ -107,6 +108,5 @@ module.exports = function (opts) {
 
   if (opts.extensions) hookExtensions(util.arrayify(opts.extensions));
 
-  if (opts.blacklist) blacklist = util.arrayify(opts.blacklist);
-  if (opts.whitelist) whitelist = util.arrayify(opts.whitelist);
+  _.extend(transformOpts, opts);
 };
diff --git a/lib/6to5/util.js b/lib/6to5/util.js
index a7d8ff8415..0a06cfa9c8 100644
--- a/lib/6to5/util.js
+++ b/lib/6to5/util.js
@@ -218,7 +218,7 @@ exports.parse = function (opts, code, callback) {
     var ast = acorn.parse(code, {
       allowReturnOutsideFunction: true,
       preserveParens:             true,
-      ecmaVersion:                Infinity,
+      ecmaVersion:                opts.experimental ? 7 : 6,
       strictMode:                 true,
       onComment:                  comments,
       locations:                  true,
diff --git a/test/fixtures/transformation/array-comprehension/options.json b/test/fixtures/transformation/array-comprehension/options.json
new file mode 100644
index 0000000000..252f473a73
--- /dev/null
+++ b/test/fixtures/transformation/array-comprehension/options.json
@@ -0,0 +1,3 @@
+{
+  "experimental": true
+}
diff --git a/test/fixtures/transformation/async/options.json b/test/fixtures/transformation/async/options.json
index 165ec035ab..8a6dc3a088 100644
--- a/test/fixtures/transformation/async/options.json
+++ b/test/fixtures/transformation/async/options.json
@@ -1,3 +1,4 @@
 {
-  "asyncExec": true
+  "asyncExec": true,
+  "experimental": true
 }
diff --git a/test/fixtures/transformation/generator-comprehension/options.json b/test/fixtures/transformation/generator-comprehension/options.json
new file mode 100644
index 0000000000..252f473a73
--- /dev/null
+++ b/test/fixtures/transformation/generator-comprehension/options.json
@@ -0,0 +1,3 @@
+{
+  "experimental": true
+}