diff --git a/src/renderers/shared/ReactInstrumentation.js b/src/renderers/shared/ReactInstrumentation.js
index 08419bc0e2..a5de36d00e 100644
--- a/src/renderers/shared/ReactInstrumentation.js
+++ b/src/renderers/shared/ReactInstrumentation.js
@@ -7,11 +7,13 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  *
  * @providesModule ReactInstrumentation
+ * @flow
  */
 
 'use strict';
 
-var debugTool = null;
+// Trust the developer to only use ReactInstrumentation with a __DEV__ check
+var debugTool = ((null: any): typeof ReactDebugTool);
 
 if (__DEV__) {
   var ReactDebugTool = require('ReactDebugTool');