diff --git a/lib/6to5/transformation/transformers/es7-abstract-references.js b/lib/6to5/transformation/transformers/es7-abstract-references.js
index 2bdf11365c..f6fa4510ba 100644
--- a/lib/6to5/transformation/transformers/es7-abstract-references.js
+++ b/lib/6to5/transformation/transformers/es7-abstract-references.js
@@ -3,6 +3,8 @@
 var util = require("../../util");
 var t    = require("../../types");
 
+exports.experimental = true;
+
 var container = function (parent, call, ret) {
   if (t.isExpressionStatement(parent)) {
     // we don't need to worry about return values
diff --git a/lib/6to5/transformation/transformers/es7-array-comprehension.js b/lib/6to5/transformation/transformers/es7-array-comprehension.js
index ded4f5a28f..40c42fca15 100644
--- a/lib/6to5/transformation/transformers/es7-array-comprehension.js
+++ b/lib/6to5/transformation/transformers/es7-array-comprehension.js
@@ -1,6 +1,8 @@
 var util = require("../../util");
 var t    = require("../../types");
 
+exports.experimental = true;
+
 var single = function (node, file) {
   var block = node.blocks[0];
 
diff --git a/lib/6to5/transformation/transformers/es7-exponentiation-operator.js b/lib/6to5/transformation/transformers/es7-exponentiation-operator.js
index af5858cdd8..f5825967ee 100644
--- a/lib/6to5/transformation/transformers/es7-exponentiation-operator.js
+++ b/lib/6to5/transformation/transformers/es7-exponentiation-operator.js
@@ -1,5 +1,7 @@
 // https://github.com/rwaldron/exponentiation-operator
 
+exports.experimental = true;
+
 var t = require("../../types");
 var pow = t.memberExpression(t.identifier("Math"), t.identifier("pow"));
 
diff --git a/lib/6to5/transformation/transformers/es7-generator-comprehension.js b/lib/6to5/transformation/transformers/es7-generator-comprehension.js
index 2034beef85..9d950fecd3 100644
--- a/lib/6to5/transformation/transformers/es7-generator-comprehension.js
+++ b/lib/6to5/transformation/transformers/es7-generator-comprehension.js
@@ -1,6 +1,8 @@
 var arrayComprehension = require("./es7-array-comprehension");
 var t                  = require("../../types");
 
+exports.experimental = true;
+
 exports.ComprehensionExpression = function (node) {
   if (!node.generator) return;
 
diff --git a/lib/6to5/transformation/transformers/es7-object-spread.js b/lib/6to5/transformation/transformers/es7-object-spread.js
index ec10d971c5..47469a35bc 100644
--- a/lib/6to5/transformation/transformers/es7-object-spread.js
+++ b/lib/6to5/transformation/transformers/es7-object-spread.js
@@ -2,6 +2,8 @@
 
 var t = require("../../types");
 
+exports.experimental = true;
+
 exports.ObjectExpression = function (node) {
   var hasSpread = false;
   var i;