diff --git a/package.json b/package.json
index e99983d9fc..940c4c08b2 100644
--- a/package.json
+++ b/package.json
@@ -45,14 +45,11 @@
     "loose": [
       "all"
     ],
-    "plugins": [
-      "flow-comments"
-    ],
     "blacklist": [
-      "flow",
       "es6.tailCall"
     ],
     "optional": [
+      "flow",
       "optimisation.flow.forOf",
       "runtime"
     ],
diff --git a/packages/babel-core/test/fixtures/transformation/misc/regression-1130/expected.js b/packages/babel-core/test/fixtures/transformation/misc/regression-1130/expected.js
index 165d31d24a..8d476ed213 100644
--- a/packages/babel-core/test/fixtures/transformation/misc/regression-1130/expected.js
+++ b/packages/babel-core/test/fixtures/transformation/misc/regression-1130/expected.js
@@ -1,7 +1,7 @@
 function A() {
-  var a = undefined;
+  var a = void 0;
 }
 
 function B() {
-  var a = undefined;
+  var a = void 0;
 }
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/for-return-undefined/expected.js b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/for-return-undefined/expected.js
index 724322adb8..3dec699cdd 100644
--- a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/for-return-undefined/expected.js
+++ b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/for-return-undefined/expected.js
@@ -4,7 +4,7 @@
       return i;
     });
     return {
-      v: undefined
+      v: void 0
     };
   };
 
diff --git a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loop-initializer-default/expected.js b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loop-initializer-default/expected.js
index 76ee5c3826..34f985252e 100644
--- a/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loop-initializer-default/expected.js
+++ b/packages/babel-plugin-transform-es2015-block-scoping/test/fixtures/general/loop-initializer-default/expected.js
@@ -1,5 +1,5 @@
 while (value) {
-  var foo = undefined;
+  var foo = void 0;
 
   if (bar) {
     foo = [];
diff --git a/packages/babel-plugin-transform-es2015-classes/test/fixtures/spec/constructor/expected.js b/packages/babel-plugin-transform-es2015-classes/test/fixtures/spec/constructor/expected.js
index 48021ec700..777d4fe01d 100644
--- a/packages/babel-plugin-transform-es2015-classes/test/fixtures/spec/constructor/expected.js
+++ b/packages/babel-plugin-transform-es2015-classes/test/fixtures/spec/constructor/expected.js
@@ -22,8 +22,8 @@ var Foo = function (_Bar) {
 var ConstructorScoping = function ConstructorScoping() {
   babelHelpers.classCallCheck(this, ConstructorScoping);
 
-  var bar = undefined;
+  var bar = void 0;
   {
-    var _bar = undefined;
+    var _bar = void 0;
   }
 };