diff --git a/packages/react-dom/src/server/ReactPartialRenderer.js b/packages/react-dom/src/server/ReactPartialRenderer.js
index e06f1df9bcd88..a28b41fc12c90 100644
--- a/packages/react-dom/src/server/ReactPartialRenderer.js
+++ b/packages/react-dom/src/server/ReactPartialRenderer.js
@@ -9,7 +9,7 @@
 
 import type {ThreadID} from './ReactThreadIDAllocator';
 import type {ReactElement} from 'shared/ReactElementType';
-import type {LazyComponent} from 'shared/ReactLazyComponent';
+import type {LazyComponent} from 'react/src/ReactLazy';
 import type {ReactProvider, ReactContext} from 'shared/ReactTypes';
 
 import * as React from 'react';
@@ -17,12 +17,8 @@ import invariant from 'shared/invariant';
 import getComponentName from 'shared/getComponentName';
 import describeComponentFrame from 'shared/describeComponentFrame';
 import ReactSharedInternals from 'shared/ReactSharedInternals';
-import {
-  Resolved,
-  Rejected,
-  Pending,
-  initializeLazyComponentType,
-} from 'shared/ReactLazyComponent';
+import {initializeLazyComponentType} from 'shared/ReactLazyComponent';
+import {Resolved, Rejected, Pending} from 'shared/ReactLazyStatusTags';
 import {
   warnAboutDeprecatedLifecycles,
   disableLegacyContext,
diff --git a/packages/react-reconciler/src/ReactFiberLazyComponent.js b/packages/react-reconciler/src/ReactFiberLazyComponent.js
index 290458eb96928..394b35ae906d8 100644
--- a/packages/react-reconciler/src/ReactFiberLazyComponent.js
+++ b/packages/react-reconciler/src/ReactFiberLazyComponent.js
@@ -7,9 +7,10 @@
  * @flow
  */
 
-import type {LazyComponent} from 'shared/ReactLazyComponent';
+import type {LazyComponent} from 'react/src/ReactLazy';
 
-import {Resolved, initializeLazyComponentType} from 'shared/ReactLazyComponent';
+import {Resolved} from 'shared/ReactLazyStatusTags';
+import {initializeLazyComponentType} from 'shared/ReactLazyComponent';
 
 export function resolveDefaultProps(Component: any, baseProps: Object): Object {
   if (Component && Component.defaultProps) {
diff --git a/packages/react/src/ReactLazy.js b/packages/react/src/ReactLazy.js
index c804c53741a60..1de3189c923c6 100644
--- a/packages/react/src/ReactLazy.js
+++ b/packages/react/src/ReactLazy.js
@@ -3,25 +3,61 @@
  *
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
  */
 
-import type {LazyComponent, Thenable} from 'shared/ReactLazyComponent';
-
 import {REACT_LAZY_TYPE} from 'shared/ReactSymbols';
 
-export function lazy<T, R>(ctor: () => Thenable<T, R>): LazyComponent<T> {
-  let lazyType = {
+type Thenable<T, R> = {
+  then(resolve: (T) => mixed, reject: (mixed) => mixed): R,
+};
+
+export type UninitializedLazyComponent<T> = {
+  $$typeof: Symbol | number,
+  _status: -1,
+  _result: () => Thenable<{default: T, ...} | T, mixed>,
+};
+
+export type PendingLazyComponent<T> = {
+  $$typeof: Symbol | number,
+  _status: 0,
+  _result: Thenable<{default: T, ...} | T, mixed>,
+};
+
+export type ResolvedLazyComponent<T> = {
+  $$typeof: Symbol | number,
+  _status: 1,
+  _result: T,
+};
+
+export type RejectedLazyComponent = {
+  $$typeof: Symbol | number,
+  _status: 2,
+  _result: mixed,
+};
+
+export type LazyComponent<T> =
+  | UninitializedLazyComponent<T>
+  | PendingLazyComponent<T>
+  | ResolvedLazyComponent<T>
+  | RejectedLazyComponent;
+
+export function lazy<T>(
+  ctor: () => Thenable<{default: T, ...} | T, mixed>,
+): LazyComponent<T> {
+  let lazyType: LazyComponent<T> = {
     $$typeof: REACT_LAZY_TYPE,
-    _ctor: ctor,
     // React uses these fields to store the result.
     _status: -1,
-    _result: null,
+    _result: ctor,
   };
 
   if (__DEV__) {
     // In production, this would just set it on the object.
     let defaultProps;
     let propTypes;
+    // $FlowFixMe
     Object.defineProperties(lazyType, {
       defaultProps: {
         configurable: true,
@@ -36,6 +72,7 @@ export function lazy<T, R>(ctor: () => Thenable<T, R>): LazyComponent<T> {
           );
           defaultProps = newDefaultProps;
           // Match production behavior more closely:
+          // $FlowFixMe
           Object.defineProperty(lazyType, 'defaultProps', {
             enumerable: true,
           });
@@ -54,6 +91,7 @@ export function lazy<T, R>(ctor: () => Thenable<T, R>): LazyComponent<T> {
           );
           propTypes = newPropTypes;
           // Match production behavior more closely:
+          // $FlowFixMe
           Object.defineProperty(lazyType, 'propTypes', {
             enumerable: true,
           });
diff --git a/packages/shared/ReactLazyComponent.js b/packages/shared/ReactLazyComponent.js
index 246ba41e83da5..24b360a1e57a1 100644
--- a/packages/shared/ReactLazyComponent.js
+++ b/packages/shared/ReactLazyComponent.js
@@ -7,35 +7,23 @@
  * @flow
  */
 
-export type Thenable<T, R> = {
-  then(resolve: (T) => mixed, reject: (mixed) => mixed): R,
-  ...
-};
+import type {
+  PendingLazyComponent,
+  ResolvedLazyComponent,
+  RejectedLazyComponent,
+  LazyComponent,
+} from 'react/src/ReactLazy';
 
-export type LazyComponent<T> = {
-  $$typeof: Symbol | number,
-  _ctor: () => Thenable<{default: T, ...}, mixed>,
-  _status: 0 | 1 | 2,
-  _result: any,
-  ...
-};
-
-type ResolvedLazyComponent<T> = {
-  $$typeof: Symbol | number,
-  _ctor: () => Thenable<{default: T, ...}, mixed>,
-  _status: 1,
-  _result: any,
-  ...
-};
-
-export const Uninitialized = -1;
-export const Pending = 0;
-export const Resolved = 1;
-export const Rejected = 2;
+import {
+  Uninitialized,
+  Pending,
+  Resolved,
+  Rejected,
+} from './ReactLazyStatusTags';
 
 export function refineResolvedLazyComponent<T>(
   lazyComponent: LazyComponent<T>,
-): ResolvedLazyComponent<T> | null {
+): T | null {
   return lazyComponent._status === Resolved ? lazyComponent._result : null;
 }
 
@@ -43,10 +31,16 @@ export function initializeLazyComponentType(
   lazyComponent: LazyComponent<any>,
 ): void {
   if (lazyComponent._status === Uninitialized) {
-    lazyComponent._status = Pending;
-    const ctor = lazyComponent._ctor;
+    let ctor = lazyComponent._result;
+    if (!ctor) {
+      // TODO: Remove this later. THis only exists in case you use an older "react" package.
+      ctor = ((lazyComponent: any)._ctor: typeof ctor);
+    }
     const thenable = ctor();
-    lazyComponent._result = thenable;
+    // Transition to the next state.
+    const pending: PendingLazyComponent<any> = (lazyComponent: any);
+    pending._status = Pending;
+    pending._result = thenable;
     thenable.then(
       moduleObject => {
         if (lazyComponent._status === Pending) {
@@ -61,14 +55,18 @@ export function initializeLazyComponentType(
               );
             }
           }
-          lazyComponent._status = Resolved;
-          lazyComponent._result = defaultExport;
+          // Transition to the next state.
+          const resolved: ResolvedLazyComponent<any> = (lazyComponent: any);
+          resolved._status = Resolved;
+          resolved._result = defaultExport;
         }
       },
       error => {
         if (lazyComponent._status === Pending) {
-          lazyComponent._status = Rejected;
-          lazyComponent._result = error;
+          // Transition to the next state.
+          const rejected: RejectedLazyComponent = (lazyComponent: any);
+          rejected._status = Rejected;
+          rejected._result = error;
         }
       },
     );
diff --git a/packages/shared/ReactLazyStatusTags.js b/packages/shared/ReactLazyStatusTags.js
new file mode 100644
index 0000000000000..8baa0ad217248
--- /dev/null
+++ b/packages/shared/ReactLazyStatusTags.js
@@ -0,0 +1,14 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow
+ */
+
+// TODO: Move this to "react" once we can import from externals.
+export const Uninitialized = -1;
+export const Pending = 0;
+export const Resolved = 1;
+export const Rejected = 2;
diff --git a/packages/shared/getComponentName.js b/packages/shared/getComponentName.js
index 9694732ce5d96..9817ea21963ee 100644
--- a/packages/shared/getComponentName.js
+++ b/packages/shared/getComponentName.js
@@ -7,7 +7,7 @@
  * @flow
  */
 
-import type {LazyComponent} from 'shared/ReactLazyComponent';
+import type {LazyComponent} from 'react/src/ReactLazy';
 
 import {
   REACT_CONTEXT_TYPE,