diff --git a/tests/extension-host/suite/index.ts b/tests/extension-host/suite/index.ts
index 297ccb98..ad0aa72a 100644
--- a/tests/extension-host/suite/index.ts
+++ b/tests/extension-host/suite/index.ts
@@ -1,12 +1,33 @@
+import * as fs from 'fs';
+import { SourceMap } from 'module';
 import * as path from 'path';
 import Mocha from 'mocha';
 import { glob } from 'glob';
 
+// The extension host formats stacks itself, ignoring source maps, so a failure's stack names the compiled files in
+// out-test. Those frames are rewritten to the TypeScript lines they were built from, which reporters then show.
+function mapStack(stack: string): string {
+  return stack.replace(
+    /out-test[\\/]suite[\\/]([^:()\s]+?)\.js:(\d+):(\d+)/g,
+    (frame, name: string, line: string, column: string) => {
+      const sourceMap = new SourceMap(
+        JSON.parse(fs.readFileSync(path.join(__dirname, `${name}.js.map`), 'utf8'))
+      );
+      const entry = sourceMap.findEntry(Number(line) - 1, Number(column) - 1);
+      if (!('originalLine' in entry)) return frame;
+      const source = `tests/extension-host/suite/${name.split(path.sep).join('/')}.ts`;
+      return `${source}:${entry.originalLine + 1}:${entry.originalColumn + 1}`;
+    }
+  );
+}
+
 export async function run(): Promise<void> {
   const mocha = new Mocha({
     ui: 'tdd', // tests use suite/test globals
     color: true,
     timeout: 20_000,
+    // On GitHub Actions, failures are also reported as annotations on the lines in their stacks.
+    reporter: process.env.GITHUB_ACTIONS === 'true' ? 'github-actions' : 'spec',
   });
 
   const testsRoot = __dirname;
@@ -15,13 +36,17 @@ export async function run(): Promise<void> {
 
   return new Promise((resolve, reject) => {
     try {
-      mocha.run((failures) => {
+      const runner = mocha.run((failures) => {
         if (failures > 0) {
           reject(new Error(`${failures} test(s) failed.`));
         } else {
           resolve();
         }
       });
+      // Reporters read a failure's stack when they print it, after the test run ends.
+      runner.on('fail', (_test, err: Error) => {
+        if (err.stack) err.stack = mapStack(err.stack);
+      });
     } catch (err) {
       reject(err as Error);
     }