diff --git a/package.json b/package.json
index 5e81c3f..4d74d8b 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@vscode/test-web",
-  "version": "0.0.26",
+  "version": "0.0.27",
   "scripts": {
     "install-extensions": "yarn --cwd=fs-provider && yarn --cwd=sample",
     "compile": "tsc -p ./ && yarn compile-fs-provider",
@@ -35,7 +35,8 @@
     "http-proxy-agent": "^5.0.0",
     "https-proxy-agent": "^5.0.1",
     "decompress": "^4.2.1",
-    "decompress-targz": "^4.1.1"
+    "decompress-targz": "^4.1.1",
+    "get-stream": "6.0.1"
   },
   "devDependencies": {
     "@types/koa": "^2.13.4",
diff --git a/src/server/app.ts b/src/server/app.ts
index b7114d1..783bd94 100644
--- a/src/server/app.ts
+++ b/src/server/app.ts
@@ -3,12 +3,14 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
+import { ReadStream } from 'fs';
 import * as Koa from 'koa';
 import * as morgan from 'koa-morgan';
 import * as kstatic from 'koa-static';
 import * as kmount from 'koa-mount';
 import * as cors from '@koa/cors';
-import { join } from 'path';
+import * as getstream from 'get-stream';
+import { basename, join } from 'path';
 import { IConfig } from './main';
 import workbench from './workbench';
 import { configureMounts } from './mounts';
@@ -42,6 +44,15 @@ export default async function createApp(config: IConfig): Promise<Koa> {
 		return next();
 	});
 
+	// shift the line numbers of source maps in extensions by 2 as the content is wrapped by an anonymous function
+	app.use(async (ctx, next) => {
+		await next();
+		if (ctx.status === 200 && ctx.path.match(/\/(dev)?extensions\/.*\.js\.map$/) && ctx.body instanceof ReadStream) {
+			// we know it's a ReadStream as that's what kstatic uses
+			ctx.response.body = `{"version":3,"file":"${basename(ctx.path)}","sections":[{"offset":{"line":2,"column":0},"map":${await getstream(ctx.body)} }]}`;
+		}
+	});
+
 	const serveOptions: kstatic.Options = { hidden: true };
 
 	if (config.extensionDevelopmentPath) {
diff --git a/yarn.lock b/yarn.lock
index 92fc5d9..ff3ce99 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -943,6 +943,11 @@ functional-red-black-tree@^1.0.1:
   resolved "https://registry.yarnpkg.com/functional-red-black-tree/-/functional-red-black-tree-1.0.1.tgz#1b0ab3bd553b2a0d6399d29c0e3ea0b252078327"
   integrity sha1-GwqzvVU7Kg1jmdKcDj6gslIHgyc=
 
+get-stream@6.0.1:
+  version "6.0.1"
+  resolved "https://registry.yarnpkg.com/get-stream/-/get-stream-6.0.1.tgz#a262d8eef67aced57c2852ad6167526a43cbf7b7"
+  integrity sha512-ts6Wi+2j3jQjqi70w5AlN8DFnkSwC+MqmxEzdEALB2qXZYV3X/b1CTfgPLGJNMeAWxdPfU8FO1ms3NUfaHCPYg==
+
 get-stream@^2.2.0:
   version "2.3.1"
   resolved "https://registry.yarnpkg.com/get-stream/-/get-stream-2.3.1.tgz#5f38f93f346009666ee0150a054167f91bdd95de"