diff --git a/src/renderers/shared/fiber/ReactFiberContext.js b/src/renderers/shared/fiber/ReactFiberContext.js
index fbc478020f..5fd47f5a18 100644
--- a/src/renderers/shared/fiber/ReactFiberContext.js
+++ b/src/renderers/shared/fiber/ReactFiberContext.js
@@ -80,23 +80,32 @@ exports.popContextProvider = function() : void {
 exports.pushContextProvider = function(fiber : Fiber, didPerformWork : boolean) : void {
   const instance = fiber.stateNode;
   const childContextTypes = fiber.type.childContextTypes;
-  const childContext = instance.getChildContext();
 
-  for (let contextKey in childContext) {
-    invariant(
-      contextKey in childContextTypes,
-      '%s.getChildContext(): key "%s" is not defined in childContextTypes.',
-      getComponentName(fiber),
-      contextKey
-    );
-  }
-  if (__DEV__) {
-    const name = getComponentName(fiber);
-    const debugID = 0; // TODO: pass a real ID
-    checkReactTypeSpec(childContextTypes, childContext, 'childContext', name, null, debugID);
+  const memoizedMergedChildContext = instance.__reactInternalMemoizedMergedChildContext;
+  const canReuseMergedChildContext = !didPerformWork && memoizedMergedChildContext != null;
+
+  let mergedContext = null;
+  if (canReuseMergedChildContext) {
+    mergedContext = memoizedMergedChildContext;
+  } else {
+    const childContext = instance.getChildContext();
+    for (let contextKey in childContext) {
+      invariant(
+        contextKey in childContextTypes,
+        '%s.getChildContext(): key "%s" is not defined in childContextTypes.',
+        getComponentName(fiber),
+        contextKey
+      );
+    }
+    if (__DEV__) {
+      const name = getComponentName(fiber);
+      const debugID = 0; // TODO: pass a real ID
+      checkReactTypeSpec(childContextTypes, childContext, 'childContext', name, null, debugID);
+    }
+    mergedContext = {...getUnmaskedContext(), ...childContext};
+    instance.__reactInternalMemoizedMergedChildContext = mergedContext;
   }
 
-  const mergedContext = Object.assign({}, getUnmaskedContext(), childContext);
   index++;
   contextStack[index] = mergedContext;
   didPerformWorkStack[index] = didPerformWork;
diff --git a/src/renderers/shared/fiber/__tests__/ReactIncremental-test.js b/src/renderers/shared/fiber/__tests__/ReactIncremental-test.js
index 14cc145254..6c5e04d010 100644
--- a/src/renderers/shared/fiber/__tests__/ReactIncremental-test.js
+++ b/src/renderers/shared/fiber/__tests__/ReactIncremental-test.js
@@ -1822,8 +1822,8 @@ describe('ReactIncremental', () => {
     statefulInst.setState({x: 1});
     ReactNoop.flush();
     expect(ops).toEqual([
-      // TODO: we should be able to reuse the previous child context.
-      'Intl:provide {"locale":"fr"}',
+      // Intl was memoized so we did not need to
+      // either render it or recompute its context.
       'ShowLocaleClass:read {"locale":"fr"}',
       'ShowLocaleFn:read {"locale":"fr"}',
     ]);
@@ -1895,6 +1895,9 @@ describe('ReactIncremental', () => {
     statefulInst.setState({locale: 'gr'});
     ReactNoop.flush();
     expect(ops).toEqual([
+      // Intl is below setState() so it might have been
+      // affected by it. Therefore we re-render and recompute
+      // its child context.
       'Intl:read null',
       'Intl:provide {"locale":"gr"}',
       'ShowLocaleClass:read {"locale":"gr"}',