diff --git a/src/core/ReactComponentEnvironment.js b/src/core/ReactComponentEnvironment.js
index 5af6a268cd..e626314ae8 100644
--- a/src/core/ReactComponentEnvironment.js
+++ b/src/core/ReactComponentEnvironment.js
@@ -15,6 +15,7 @@
  *
  * @providesModule ReactComponentEnvironment
  */
+"use strict";
 
 var ReactComponentBrowserEnvironment =
   require('ReactComponentBrowserEnvironment');
diff --git a/src/core/ReactMultiChildUpdateTypes.js b/src/core/ReactMultiChildUpdateTypes.js
index 046eaaae93..3d9297754b 100644
--- a/src/core/ReactMultiChildUpdateTypes.js
+++ b/src/core/ReactMultiChildUpdateTypes.js
@@ -15,6 +15,7 @@
  *
  * @providesModule ReactMultiChildUpdateTypes
  */
+"use strict";
 
 var keyMirror = require('keyMirror');