diff --git a/DeviceDescriptors.js b/DeviceDescriptors.js
index 2ac295c3ba..5b4ab87e1c 100644
--- a/DeviceDescriptors.js
+++ b/DeviceDescriptors.js
@@ -17,7 +17,4 @@
 
 const {DeviceDescriptors} = require('./lib/deviceDescriptors');
 
-const descriptors = DeviceDescriptors.slice();
-module.exports = descriptors;
-for (const device of descriptors)
-  module.exports[device.name] = device;
+module.exports = DeviceDescriptors;
diff --git a/src/chromium/crPlaywright.ts b/src/chromium/crPlaywright.ts
index d14f3bb256..880475ff5d 100644
--- a/src/chromium/crPlaywright.ts
+++ b/src/chromium/crPlaywright.ts
@@ -20,15 +20,14 @@ import * as https from 'https';
 import * as URL from 'url';
 import * as browsers from '../browser';
 import { BrowserFetcher, BrowserFetcherOptions, BrowserFetcherRevisionInfo, OnProgressCallback } from '../browserFetcher';
-import { DeviceDescriptor, DeviceDescriptors } from '../deviceDescriptors';
+import { DeviceDescriptors } from '../deviceDescriptors';
 import * as Errors from '../errors';
+import * as types from '../types';
 import { assert } from '../helper';
 import { ConnectionTransport, WebSocketTransport, SlowMoTransport } from '../transport';
 import { ConnectionOptions, createBrowserFetcher, CRLauncher, LauncherChromeArgOptions, LauncherLaunchOptions } from './crLauncher';
 import { CRBrowser } from './crBrowser';
 
-type Devices = { [name: string]: DeviceDescriptor } & DeviceDescriptor[];
-
 export class CRPlaywright {
   private _projectRoot: string;
   private _launcher: CRLauncher;
@@ -80,11 +79,8 @@ export class CRPlaywright {
     return this._launcher.executablePath();
   }
 
-  get devices(): Devices {
-    const result = DeviceDescriptors.slice() as Devices;
-    for (const device of DeviceDescriptors)
-      result[device.name] = device;
-    return result;
+  get devices(): types.Devices {
+    return DeviceDescriptors;
   }
 
   get errors(): any {
diff --git a/src/deviceDescriptors.ts b/src/deviceDescriptors.ts
index e387a309ab..0697a0cbc2 100644
--- a/src/deviceDescriptors.ts
+++ b/src/deviceDescriptors.ts
@@ -17,13 +17,7 @@
 
 import * as types from './types';
 
-export type DeviceDescriptor = {
-  name: string,
-  userAgent: string,
-  viewport: types.Viewport,
-};
-
-export const DeviceDescriptors: DeviceDescriptor[] = [
+const descriptors: types.DeviceDescriptor[] = [
   {
     'name': 'Blackberry PlayBook',
     'userAgent': 'Mozilla/5.0 (PlayBook; U; RIM Tablet OS 2.1.0; en-US) AppleWebKit/536.2+ (KHTML like Gecko) Version/7.2.1.0 Safari/536.2+',
@@ -877,3 +871,7 @@ export const DeviceDescriptors: DeviceDescriptor[] = [
     }
   }
 ];
+
+export const DeviceDescriptors = descriptors as types.Devices;
+for (const device of descriptors)
+  DeviceDescriptors[device.name] = device;
diff --git a/src/firefox/ffPlaywright.ts b/src/firefox/ffPlaywright.ts
index fdf716fe0a..c6a5aaf988 100644
--- a/src/firefox/ffPlaywright.ts
+++ b/src/firefox/ffPlaywright.ts
@@ -19,12 +19,11 @@ import * as browsers from '../browser';
 import { FFBrowser } from './ffBrowser';
 import { BrowserFetcher, BrowserFetcherOptions, OnProgressCallback, BrowserFetcherRevisionInfo } from '../browserFetcher';
 import { WebSocketTransport, SlowMoTransport } from '../transport';
-import { DeviceDescriptors, DeviceDescriptor } from '../deviceDescriptors';
+import { DeviceDescriptors } from '../deviceDescriptors';
 import * as Errors from '../errors';
+import * as types from '../types';
 import { FFLauncher, createBrowserFetcher } from './ffLauncher';
 
-type Devices = { [name: string]: DeviceDescriptor } & DeviceDescriptor[];
-
 export class FFPlaywright {
   private _projectRoot: string;
   private _launcher: FFLauncher;
@@ -61,11 +60,8 @@ export class FFPlaywright {
     return this._launcher.executablePath();
   }
 
-  get devices(): Devices {
-    const result = DeviceDescriptors.slice() as Devices;
-    for (const device of DeviceDescriptors)
-      result[device.name] = device;
-    return result;
+  get devices(): types.Devices {
+    return DeviceDescriptors;
   }
 
   get errors(): any {
diff --git a/src/types.ts b/src/types.ts
index 49fd3a4436..1ead5a50fc 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -92,3 +92,10 @@ export const mediaTypes: Set<MediaType> = new Set(['screen', 'print']);
 
 export type ColorScheme = 'dark' | 'light' | 'no-preference';
 export const colorSchemes: Set<ColorScheme> = new Set(['dark', 'light', 'no-preference']);
+
+export type DeviceDescriptor = {
+  name: string,
+  userAgent: string,
+  viewport: Viewport,
+};
+export type Devices = { [name: string]: DeviceDescriptor } & DeviceDescriptor[];
diff --git a/src/webkit/wkPlaywright.ts b/src/webkit/wkPlaywright.ts
index f71c3d30eb..d7422133ba 100644
--- a/src/webkit/wkPlaywright.ts
+++ b/src/webkit/wkPlaywright.ts
@@ -18,6 +18,7 @@ import * as browsers from '../browser';
 import { BrowserFetcher, BrowserFetcherOptions, OnProgressCallback, BrowserFetcherRevisionInfo } from '../browserFetcher';
 import { DeviceDescriptors } from '../deviceDescriptors';
 import * as Errors from '../errors';
+import * as types from '../types';
 import { WKLauncher, LauncherLaunchOptions, createBrowserFetcher } from './wkLauncher';
 import { WKBrowser } from './wkBrowser';
 
@@ -52,11 +53,8 @@ export class WKPlaywright {
     return this._launcher.executablePath();
   }
 
-  get devices(): any {
-    const result = DeviceDescriptors.slice();
-    for (const device of DeviceDescriptors)
-      result[device.name] = device;
-    return result;
+  get devices(): types.Devices {
+    return DeviceDescriptors;
   }
 
   get errors(): any {