diff --git a/src/core/ReactComponentEnvironment.js b/src/core/ReactComponentEnvironment.js
index 5af6a268cd..78bdd1b63b 100644
--- a/src/core/ReactComponentEnvironment.js
+++ b/src/core/ReactComponentEnvironment.js
@@ -16,6 +16,8 @@
  * @providesModule ReactComponentEnvironment
  */
 
+"use strict";
+
 var ReactComponentBrowserEnvironment =
   require('ReactComponentBrowserEnvironment');
 
diff --git a/src/core/ReactMultiChildUpdateTypes.js b/src/core/ReactMultiChildUpdateTypes.js
index 046eaaae93..179dca2c37 100644
--- a/src/core/ReactMultiChildUpdateTypes.js
+++ b/src/core/ReactMultiChildUpdateTypes.js
@@ -16,6 +16,8 @@
  * @providesModule ReactMultiChildUpdateTypes
  */
 
+"use strict";
+
 var keyMirror = require('keyMirror');
 
 /**
diff --git a/src/core/__tests__/ReactMultiChild-test.js b/src/core/__tests__/ReactMultiChild-test.js
index 6614ec5a53..914b8b1733 100644
--- a/src/core/__tests__/ReactMultiChild-test.js
+++ b/src/core/__tests__/ReactMultiChild-test.js
@@ -17,6 +17,8 @@
  * @emails react-core
  */
 
+"use strict";
+
 var mocks = require('mocks');
 
 describe('ReactMultiChild', function() {
diff --git a/src/dom/__tests__/Danger-test.js b/src/dom/__tests__/Danger-test.js
index f82a97241e..5086a8f279 100644
--- a/src/dom/__tests__/Danger-test.js
+++ b/src/dom/__tests__/Danger-test.js
@@ -16,9 +16,10 @@
  * @jsx React.DOM
  * @emails react-core
  */
-
 /*jslint evil: true */
 
+"use strict";
+
 var React = require('React');
 
 describe('Danger', function() {