diff --git a/build/npm/postinstall.js b/build/npm/postinstall.js
new file mode 100644
index 00000000000..207eee30393
--- /dev/null
+++ b/build/npm/postinstall.js
@@ -0,0 +1,22 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+const cp = require('child_process');
+
+const extensions = [
+	'vscode-api-tests',
+	'vscode-colorize-tests',
+	'json',
+	'typescript',
+	'php',
+	'javascript'
+];
+
+extensions.forEach(extension => {
+	cp.spawnSync('npm', ['install'], {
+		cwd: `extensions/${ extension }`,
+		stdio: 'inherit'
+	});
+});
diff --git a/package.json b/package.json
index 51706fcb6ee..69ee54af8dd 100644
--- a/package.json
+++ b/package.json
@@ -13,7 +13,7 @@
   "scripts": {
     "test": "mocha",
     "preinstall": "node build/npm/preinstall.js",
-    "postinstall": "npm --prefix extensions/vscode-api-tests/ install extensions/vscode-api-tests/ && npm --prefix extensions/vscode-colorize-tests/ install extensions/vscode-colorize-tests/ && npm --prefix extensions/json/ install extensions/json/ && npm --prefix extensions/typescript/ install extensions/typescript/ && npm --prefix extensions/php/ install extensions/php/ && npm --prefix extensions/javascript/ install extensions/javascript/",
+    "postinstall": "node build/npm/postinstall.js",
     "watch": "gulp watch"
   },
   "dependencies": {