diff --git a/src/renderers/shared/fiber/ReactChildFiber.js b/src/renderers/shared/fiber/ReactChildFiber.js
index 699b0e7883..7d9fe2e1d1 100644
--- a/src/renderers/shared/fiber/ReactChildFiber.js
+++ b/src/renderers/shared/fiber/ReactChildFiber.js
@@ -236,11 +236,10 @@ function cloneSiblings(current : Fiber, workInProgress : Fiber, returnFiber : Fi
   workInProgress.sibling = null;
 }
 
-exports.cloneChildFibers = function(workInProgress : Fiber) {
+exports.cloneChildFibers = function(current : ?Fiber, workInProgress : Fiber) {
   if (!workInProgress.child) {
     return;
   }
-  const current = workInProgress.alternate;
   if (!current || workInProgress.child !== current.child) {
     // If there is no alternate, then we don't need to clone the children.
     // If the children of the alternate fiber is a different set, then we don't
diff --git a/src/renderers/shared/fiber/ReactFiberBeginWork.js b/src/renderers/shared/fiber/ReactFiberBeginWork.js
index feabc7838b..a21bd4059a 100644
--- a/src/renderers/shared/fiber/ReactFiberBeginWork.js
+++ b/src/renderers/shared/fiber/ReactFiberBeginWork.js
@@ -166,15 +166,15 @@ module.exports = function<T, P, I, C>(config : HostConfig<T, P, I, C>) {
     if (typeof value === 'object' && value && typeof value.render === 'function') {
       // Proceed under the assumption that this is a class instance
       workInProgress.tag = ClassComponent;
-      if (workInProgress.alternate) {
-        workInProgress.alternate.tag = ClassComponent;
+      if (current) {
+        current.tag = ClassComponent;
       }
       value = value.render();
     } else {
       // Proceed under the assumption that this is a functional component
       workInProgress.tag = FunctionalComponent;
-      if (workInProgress.alternate) {
-        workInProgress.alternate.tag = FunctionalComponent;
+      if (current) {
+        current.tag = FunctionalComponent;
       }
     }
     reconcileChildren(current, workInProgress, value);
@@ -225,7 +225,7 @@ module.exports = function<T, P, I, C>(config : HostConfig<T, P, I, C>) {
     //   return null;
     // }
 
-    cloneChildFibers(workInProgress);
+    cloneChildFibers(current, workInProgress);
     markChildAsProgressed(current, workInProgress, priorityLevel);
     return workInProgress.child;
   }
diff --git a/src/renderers/shared/fiber/ReactFiberCommitWork.js b/src/renderers/shared/fiber/ReactFiberCommitWork.js
index c7a9f2f710..2e3e8ae3d0 100644
--- a/src/renderers/shared/fiber/ReactFiberCommitWork.js
+++ b/src/renderers/shared/fiber/ReactFiberCommitWork.js
@@ -28,7 +28,7 @@ module.exports = function<T, P, I, C>(config : HostConfig<T, P, I, C>) {
   const updateContainer = config.updateContainer;
   const commitUpdate = config.commitUpdate;
 
-  function commitWork(finishedWork : Fiber) : void {
+  function commitWork(current : ?Fiber, finishedWork : Fiber) : void {
     switch (finishedWork.tag) {
       case ClassComponent: {
         // TODO: Fire componentDidMount/componentDidUpdate, update refs
@@ -43,14 +43,13 @@ module.exports = function<T, P, I, C>(config : HostConfig<T, P, I, C>) {
         return;
       }
       case HostComponent: {
-        if (finishedWork.stateNode == null || !finishedWork.alternate) {
+        if (finishedWork.stateNode == null || !current) {
           throw new Error('This should only be done during updates.');
         }
         // Commit the work prepared earlier.
         const child = finishedWork.child;
         const children = (child && !child.sibling) ? (child.output : ?Fiber | I) : child;
         const newProps = finishedWork.memoizedProps;
-        const current = finishedWork.alternate;
         const oldProps = current.memoizedProps;
         const instance : I = finishedWork.stateNode;
         commitUpdate(instance, oldProps, newProps, children);
diff --git a/src/renderers/shared/fiber/ReactFiberScheduler.js b/src/renderers/shared/fiber/ReactFiberScheduler.js
index 057f9f7455..e04c846f20 100644
--- a/src/renderers/shared/fiber/ReactFiberScheduler.js
+++ b/src/renderers/shared/fiber/ReactFiberScheduler.js
@@ -89,7 +89,8 @@ module.exports = function<T, P, I, C>(config : HostConfig<T, P, I, C>) {
     // TODO: Error handling.
     let effectfulFiber = finishedWork.firstEffect;
     while (effectfulFiber) {
-      commitWork(effectfulFiber);
+      const current = effectfulFiber.alternate;
+      commitWork(current, effectfulFiber);
       const next = effectfulFiber.nextEffect;
       // Ensure that we clean these up so that we don't accidentally keep them.
       // I'm not actually sure this matters because we can't reset firstEffect