diff --git a/flow-typed/npm/react-test-renderer_v16.x.x.js b/flow-typed/npm/react-test-renderer_v16.x.x.js
new file mode 100644
index 0000000000..87a149a1d3
--- /dev/null
+++ b/flow-typed/npm/react-test-renderer_v16.x.x.js
@@ -0,0 +1,81 @@
+// flow-typed signature: b6bb53397d83d2d821e258cc73818d1b
+// flow-typed version: 9c71eca8ef/react-test-renderer_v16.x.x/flow_>=v0.47.x
+
+// Type definitions for react-test-renderer 16.x.x
+// Ported from: https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/react-test-renderer
+
+type ReactComponentInstance = React$Component<any>;
+
+type ReactTestRendererJSON = {
+  type: string,
+  props: { [propName: string]: any },
+  children: null | ReactTestRendererJSON[],
+};
+
+type ReactTestRendererTree = ReactTestRendererJSON & {
+  nodeType: 'component' | 'host',
+  instance: ?ReactComponentInstance,
+  rendered: null | ReactTestRendererTree,
+};
+
+type ReactTestInstance = {
+  instance: ?ReactComponentInstance,
+  type: string,
+  props: { [propName: string]: any },
+  parent: null | ReactTestInstance,
+  children: Array<ReactTestInstance | string>,
+
+  find(predicate: (node: ReactTestInstance) => boolean): ReactTestInstance,
+  findByType(type: React$ElementType): ReactTestInstance,
+  findByProps(props: { [propName: string]: any }): ReactTestInstance,
+
+  findAll(
+    predicate: (node: ReactTestInstance) => boolean,
+    options?: { deep: boolean }
+  ): ReactTestInstance[],
+  findAllByType(
+    type: React$ElementType,
+    options?: { deep: boolean }
+  ): ReactTestInstance[],
+  findAllByProps(
+    props: { [propName: string]: any },
+    options?: { deep: boolean }
+  ): ReactTestInstance[],
+};
+
+type TestRendererOptions = {
+  createNodeMock(element: React$Element<any>): any,
+};
+
+declare module 'react-test-renderer' {
+  declare export type ReactTestRenderer = {
+    toJSON(): null | ReactTestRendererJSON,
+    toTree(): null | ReactTestRendererTree,
+    unmount(nextElement?: React$Element<any>): void,
+    update(nextElement: React$Element<any>): void,
+    getInstance(): ?ReactComponentInstance,
+    root: ReactTestInstance,
+  };
+
+  declare type Thenable = {
+    then(resolve: () => mixed, reject?: () => mixed): mixed,
+  };
+
+  declare function create(
+    nextElement: React$Element<any>,
+    options?: TestRendererOptions
+  ): ReactTestRenderer;
+
+  declare function act(callback: () => void): Thenable;
+}
+
+declare module 'react-test-renderer/shallow' {
+  declare export default class ShallowRenderer {
+    static createRenderer(): ShallowRenderer;
+    getMountedInstance(): ReactTestInstance;
+    getRenderOutput<E: React$Element<any>>(): E;
+    getRenderOutput(): React$Element<any>;
+    render(element: React$Element<any>, context?: any): void;
+    unmount(): void;
+  }
+}
diff --git a/src/__tests__/profiling-test.js b/src/__tests__/profiling-test.js
index de2d4cf04c..5bd2e037bb 100644
--- a/src/__tests__/profiling-test.js
+++ b/src/__tests__/profiling-test.js
@@ -1,12 +1,17 @@
 // @flow
 
+import type React from 'react';
+import type ReactDOM from 'react-dom';
+import typeof ReactTestRenderer from 'react-test-renderer';
+import type Store from 'src/devtools/store';
+
 describe('profiling', () => {
-  let React;
-  let ReactDOM;
+  let React: React;
+  let ReactDOM: ReactDOM;
   let Scheduler;
   let SchedulerTracing;
-  let TestRenderer;
-  let store;
+  let TestRenderer: ReactTestRenderer;
+  let store: Store;
   let utils;
 
   beforeEach(() => {
@@ -161,17 +166,21 @@ describe('profiling', () => {
       const rootID = store.roots[0];
 
       for (let index = 0; index < store.numElements; index++) {
-        await utils.actSuspense(() =>
+        await utils.actSuspense(() => {
+          const fiberID = store.getElementIDAtIndex(index);
+          if (fiberID == null) {
+            throw Error(`Unexpected null ID for element at index ${index}`);
+          }
           TestRenderer.create(
             <React.Suspense fallback={null}>
               <Suspender
-                fiberID={store.getElementIDAtIndex(index)}
+                fiberID={fiberID}
                 rendererID={rendererID}
                 rootID={rootID}
               />
             </React.Suspense>
-          )
-        );
+          );
+        });
       }
 
       done();
diff --git a/src/__tests__/utils.js b/src/__tests__/utils.js
index cb15590ee5..1e3acc55ac 100644
--- a/src/__tests__/utils.js
+++ b/src/__tests__/utils.js
@@ -1,5 +1,7 @@
 // @flow
 
+import typeof ReactTestRenderer from 'react-test-renderer';
+
 export function act(callback: Function): void {
   const TestUtils = require('react-dom/test-utils');
   TestUtils.act(() => {
@@ -10,7 +12,7 @@ export function act(callback: Function): void {
   jest.runAllTimers();
 }
 
-export async function actSuspense(callback: Function) {
+export async function actSuspense(callback: Function): Promise<void> {
   const TestUtils = require('react-dom/test-utils');
   const Scheduler = require('scheduler');
 
@@ -26,7 +28,7 @@ export async function actSuspense(callback: Function) {
   Scheduler.flushAll();
 }
 
-export function beforeEachProfiling() {
+export function beforeEachProfiling(): void {
   // Mock React's timing information so that test runs are predictable.
   jest.mock('scheduler', () =>
     // $FlowFixMe Flow does not konw about requireActual
@@ -41,7 +43,7 @@ export function beforeEachProfiling() {
   );
 }
 
-export function getRendererID() {
+export function getRendererID(): number {
   if (global.agent == null) {
     throw Error('Agent unavailable.');
   }
@@ -49,10 +51,10 @@ export function getRendererID() {
   if (ids.length !== 1) {
     throw Error('Multiple renderers attached.');
   }
-  return ids[0];
+  return parseInt(ids[0], 10);
 }
 
-export function requireTestRenderer() {
+export function requireTestRenderer(): ReactTestRenderer {
   let hook;
   try {
     // Hide the hook before requiring TestRenderer, so we don't end up with a loop.