diff --git a/src/Launcher.js b/src/Launcher.js
index b046f8c33b55c..85f217c93f577 100644
--- a/src/Launcher.js
+++ b/src/Launcher.js
@@ -29,7 +29,7 @@ const {helper, assert, debugError} = require('./helper');
 const debugLauncher = require('debug')(`puppeteer:launcher`);
 const {TimeoutError} = require('./Errors');
 const WebSocketTransport = require('./WebSocketTransport');
-const PipeTransport = require('./PipeTransport');
+const {PipeTransport} = require('./PipeTransport');
 
 const mkdtempAsync = helper.promisify(fs.mkdtemp);
 const removeFolderAsync = helper.promisify(removeFolder);
diff --git a/src/PipeTransport.js b/src/PipeTransport.ts
similarity index 78%
rename from src/PipeTransport.js
rename to src/PipeTransport.ts
index fb87a97d2193e..d23ef0965173b 100644
--- a/src/PipeTransport.js
+++ b/src/PipeTransport.ts
@@ -13,17 +13,18 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
-const {helper, debugError} = require('./helper');
+import helperUtils = require('./helper');
+const {helper, debugError} = helperUtils;
 
-/**
- * @implements {!Puppeteer.ConnectionTransport}
- */
-class PipeTransport {
-  /**
-   * @param {!NodeJS.WritableStream} pipeWrite
-   * @param {!NodeJS.ReadableStream} pipeRead
-   */
-  constructor(pipeWrite, pipeRead) {
+class PipeTransport implements Puppeteer.ConnectionTransport {
+  _pipeWrite: NodeJS.WritableStream;
+  _pendingMessage: string;
+  _eventListeners: PuppeteerEventListener[];
+
+  onclose?: () => void;
+  onmessage?: () => void;
+
+  constructor(pipeWrite: NodeJS.WritableStream, pipeRead: NodeJS.ReadableStream) {
     this._pipeWrite = pipeWrite;
     this._pendingMessage = '';
     this._eventListeners = [
@@ -39,18 +40,12 @@ class PipeTransport {
     this.onclose = null;
   }
 
-  /**
-   * @param {string} message
-   */
-  send(message) {
+  send(message: string): void {
     this._pipeWrite.write(message);
     this._pipeWrite.write('\0');
   }
 
-  /**
-   * @param {!Buffer} buffer
-   */
-  _dispatch(buffer) {
+  _dispatch(buffer: Buffer): void {
     let end = buffer.indexOf('\0');
     if (end === -1) {
       this._pendingMessage += buffer.toString();
@@ -71,10 +66,10 @@ class PipeTransport {
     this._pendingMessage = buffer.toString(undefined, start);
   }
 
-  close() {
+  close(): void {
     this._pipeWrite = null;
     helper.removeEventListeners(this._eventListeners);
   }
 }
 
-module.exports = PipeTransport;
+export = {PipeTransport};
diff --git a/src/helper.ts b/src/helper.ts
index f81db28e1d29e..c5788b8083d6a 100644
--- a/src/helper.ts
+++ b/src/helper.ts
@@ -103,7 +103,7 @@ function installAsyncStackHooks(classType: AnyClass): void {
 }
 
 
-function addEventListener(emitter: NodeJS.EventEmitter, eventName: string|symbol, handler: (...args: any[]) => void): { emitter: NodeJS.EventEmitter; eventName: string|symbol; handler: (...args: any[]) => void} {
+function addEventListener(emitter: NodeJS.EventEmitter, eventName: string|symbol, handler: (...args: any[]) => void): PuppeteerEventListener {
   emitter.on(eventName, handler);
   return { emitter, eventName, handler };
 }
diff --git a/src/types.d.ts b/src/types.d.ts
new file mode 100644
index 0000000000000..8be41bae854cd
--- /dev/null
+++ b/src/types.d.ts
@@ -0,0 +1,25 @@
+/**
+ * Copyright 2020 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/* These types exist here until we migrate over to ESM where we can
+ * import / export them properly from modules - TS doesn't support
+ * exposing interfaces in CommonJS land.
+ */
+interface PuppeteerEventListener {
+  emitter: NodeJS.EventEmitter;
+  eventName: string | symbol;
+  handler: (...args: any[]) => void;
+}