diff --git a/src/renderers/shared/fiber/ReactFiberClassComponent.js b/src/renderers/shared/fiber/ReactFiberClassComponent.js
index 5e5c18f81e..4a8c27308b 100644
--- a/src/renderers/shared/fiber/ReactFiberClassComponent.js
+++ b/src/renderers/shared/fiber/ReactFiberClassComponent.js
@@ -23,6 +23,7 @@ var {
   addCallbackToQueue,
   mergeUpdateQueue,
 } = require('ReactFiberUpdateQueue');
+var { isMounted } = require('ReactFiberTreeReflection');
 var ReactInstanceMap = require('ReactInstanceMap');
 
 module.exports = function(scheduleUpdate : (fiber: Fiber, priorityLevel : PriorityLevel) => void) {
@@ -39,6 +40,7 @@ module.exports = function(scheduleUpdate : (fiber: Fiber, priorityLevel : Priori
 
   // Class component state updater
   const updater = {
+    isMounted,
     enqueueSetState(instance, partialState) {
       const fiber = ReactInstanceMap.get(instance);
       const updateQueue = fiber.updateQueue ?
diff --git a/src/renderers/shared/fiber/ReactFiberTreeReflection.js b/src/renderers/shared/fiber/ReactFiberTreeReflection.js
index 8fddb2fec1..45e2bebb5b 100644
--- a/src/renderers/shared/fiber/ReactFiberTreeReflection.js
+++ b/src/renderers/shared/fiber/ReactFiberTreeReflection.js
@@ -23,6 +23,17 @@ var {
   HostText,
 } = require('ReactTypeOfWork');
 
+exports.isMounted = function(component : ReactComponent<any, any, any>) : boolean {
+  var parent : ?Fiber = ReactInstanceMap.get(component);
+  if (!parent) {
+    return false;
+  }
+  // TODO: This doesn't deal with the case where it has completed but not yet
+  // committed. It also doesn't deal with unmounts since they currently don't
+  // clean up the item in the ReactInstanceMap.
+  return true;
+};
+
 exports.findCurrentHostFiber = function(component : ReactComponent<any, any, any>) : Fiber | null {
   var parent : ?Fiber = ReactInstanceMap.get(component);
   if (!parent) {