diff --git a/e2e/__tests__/jestChangedFiles.test.js b/e2e/__tests__/jestChangedFiles.test.js
index 6020514f44f3..8af8e70c1f41 100644
--- a/e2e/__tests__/jestChangedFiles.test.js
+++ b/e2e/__tests__/jestChangedFiles.test.js
@@ -9,14 +9,14 @@
 
 import os from 'os';
 import path from 'path';
+import {wrap} from 'jest-snapshot-serializer-raw';
 import {
   findRepos,
   getChangedFilesForRoots,
-} from '../../packages/jest-changed-files/src';
+} from '../../packages/jest-changed-files';
 import {skipSuiteOnWindows} from '../../scripts/ConditionalTest';
 import {cleanup, run, writeFiles} from '../Utils';
 import runJest from '../runJest';
-import {wrap} from 'jest-snapshot-serializer-raw';
 
 skipSuiteOnWindows();
 
diff --git a/packages/jest-changed-files/package.json b/packages/jest-changed-files/package.json
index de3d1e78442a..6aafc1373de5 100644
--- a/packages/jest-changed-files/package.json
+++ b/packages/jest-changed-files/package.json
@@ -8,6 +8,7 @@
   },
   "license": "MIT",
   "main": "build/index.js",
+  "types": "build/index.d.ts",
   "dependencies": {
     "execa": "^1.0.0",
     "throat": "^4.0.0"
diff --git a/packages/jest-changed-files/src/git.js b/packages/jest-changed-files/src/git.ts
similarity index 91%
rename from packages/jest-changed-files/src/git.js
rename to packages/jest-changed-files/src/git.ts
index 8d405ce593a4..a766bd6b5a3e 100644
--- a/packages/jest-changed-files/src/git.js
+++ b/packages/jest-changed-files/src/git.ts
@@ -4,15 +4,13 @@
  * 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 {Path} from 'types/Config';
-import type {Options, SCMAdapter} from 'types/ChangedFiles';
-
 import path from 'path';
 import execa from 'execa';
 
+import {Path, Options, SCMAdapter} from './types';
+
 const findChangedFilesUsingCommand = async (
   args: Array<string>,
   cwd: Path,
@@ -30,7 +28,7 @@ const adapter: SCMAdapter = {
     cwd: string,
     options?: Options,
   ): Promise<Array<Path>> => {
-    const changedSince: ?string =
+    const changedSince: string | null | undefined =
       options && (options.withAncestor ? 'HEAD^' : options.changedSince);
 
     const includePaths: Array<Path> = (options && options.includePaths) || [];
@@ -72,7 +70,7 @@ const adapter: SCMAdapter = {
     }
   },
 
-  getRoot: async (cwd: string): Promise<?string> => {
+  getRoot: async (cwd: string): Promise<string | null | undefined> => {
     const options = ['rev-parse', '--show-toplevel'];
 
     try {
diff --git a/packages/jest-changed-files/src/hg.js b/packages/jest-changed-files/src/hg.ts
similarity index 87%
rename from packages/jest-changed-files/src/hg.js
rename to packages/jest-changed-files/src/hg.ts
index 9459619fcc6c..0b3b3ecf7963 100644
--- a/packages/jest-changed-files/src/hg.js
+++ b/packages/jest-changed-files/src/hg.ts
@@ -4,16 +4,14 @@
  * 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 {Path} from 'types/Config';
-import type {Options, SCMAdapter} from 'types/ChangedFiles';
-
 import path from 'path';
 import execa from 'execa';
 
-const env = {...process.env, HGPLAIN: 1};
+import {Path, Options, SCMAdapter} from './types';
+
+const env = {...process.env, HGPLAIN: '1'};
 
 const ANCESTORS = [
   // Parent commit to this one.
@@ -51,7 +49,7 @@ const adapter: SCMAdapter = {
       .map(changedPath => path.resolve(cwd, changedPath));
   },
 
-  getRoot: async (cwd: Path): Promise<?Path> => {
+  getRoot: async (cwd: Path): Promise<Path | null | undefined> => {
     try {
       const result = await execa('hg', ['root'], {cwd, env});
 
diff --git a/packages/jest-changed-files/src/index.js b/packages/jest-changed-files/src/index.ts
similarity index 65%
rename from packages/jest-changed-files/src/index.js
rename to packages/jest-changed-files/src/index.ts
index f7ecf3d8fb1d..d3c160e683ee 100644
--- a/packages/jest-changed-files/src/index.js
+++ b/packages/jest-changed-files/src/index.ts
@@ -4,25 +4,23 @@
  * 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 {Path} from 'types/Config';
-import type {ChangedFilesPromise, Options, Repos} from 'types/ChangedFiles';
+import throat from 'throat';
 
+import {Path, ChangedFilesPromise, Options, Repos} from './types';
 import git from './git';
 import hg from './hg';
-import throat from 'throat';
 
 // This is an arbitrary number. The main goal is to prevent projects with
 // many roots (50+) from spawning too many processes at once.
 const mutex = throat(5);
 
-const findGitRoot = dir => mutex(() => git.getRoot(dir));
-const findHgRoot = dir => mutex(() => hg.getRoot(dir));
+const findGitRoot = (dir: string) => mutex(() => git.getRoot(dir));
+const findHgRoot = (dir: string) => mutex(() => hg.getRoot(dir));
 
 export const getChangedFilesForRoots = async (
-  roots: Array<Path>,
+  roots: Path[],
   options: Options,
 ): ChangedFilesPromise => {
   const repos = await findRepos(roots);
@@ -50,16 +48,22 @@ export const getChangedFilesForRoots = async (
   return {changedFiles, repos};
 };
 
-export const findRepos = async (roots: Array<Path>): Promise<Repos> => {
+export const findRepos = async (roots: Path[]): Promise<Repos> => {
   const gitRepos = await Promise.all(
-    roots.reduce((promises, root) => promises.concat(findGitRoot(root)), []),
+    roots.reduce<Promise<string | null | undefined>[]>(
+      (promises, root) => promises.concat(findGitRoot(root)),
+      [],
+    ),
   );
   const hgRepos = await Promise.all(
-    roots.reduce((promises, root) => promises.concat(findHgRoot(root)), []),
+    roots.reduce<Promise<string | null | undefined>[]>(
+      (promises, root) => promises.concat(findHgRoot(root)),
+      [],
+    ),
   );
 
   return {
-    git: new Set(gitRepos.filter(Boolean)),
-    hg: new Set(hgRepos.filter(Boolean)),
+    git: new Set(gitRepos.filter(Boolean) as string[]),
+    hg: new Set(hgRepos.filter(Boolean) as string[]),
   };
 };
diff --git a/packages/jest-changed-files/src/types.ts b/packages/jest-changed-files/src/types.ts
new file mode 100644
index 000000000000..36bde410b70b
--- /dev/null
+++ b/packages/jest-changed-files/src/types.ts
@@ -0,0 +1,28 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+
+export type Path = string;
+
+export type Options = {
+  lastCommit?: boolean;
+  withAncestor?: boolean;
+  changedSince?: string;
+  includePaths?: Array<Path>;
+};
+
+export type ChangedFiles = Set<Path>;
+export type Repos = {git: Set<Path>; hg: Set<Path>};
+export type ChangedFilesPromise = Promise<{
+  repos: Repos;
+  changedFiles: ChangedFiles;
+}>;
+
+export type SCMAdapter = {
+  findChangedFiles: (cwd: Path, options: Options) => Promise<Array<Path>>;
+  getRoot: (cwd: Path) => Promise<Path | null | undefined>;
+};
diff --git a/packages/jest-changed-files/tsconfig.json b/packages/jest-changed-files/tsconfig.json
new file mode 100644
index 000000000000..7bb06bce6d20
--- /dev/null
+++ b/packages/jest-changed-files/tsconfig.json
@@ -0,0 +1,7 @@
+{
+  "extends": "../../tsconfig.json",
+  "compilerOptions": {
+    "rootDir": "src",
+    "outDir": "build"
+  }
+}