diff --git a/packages/cli/src/browser/launch.boundedClose.test.ts b/packages/cli/src/browser/launch.boundedClose.test.ts
index 7607926b27..4e59b81d71 100644
--- a/packages/cli/src/browser/launch.boundedClose.test.ts
+++ b/packages/cli/src/browser/launch.boundedClose.test.ts
@@ -1,9 +1,20 @@
 import { spawn } from "node:child_process";
 import { once } from "node:events";
 import type { Browser, LaunchOptions, PuppeteerNode } from "puppeteer-core";
-import { expect, it } from "vitest";
+import { afterEach, expect, it, vi } from "vitest";
 import { launchManagedBrowser } from "./launch.js";
 
+const treeKill = vi.hoisted(() => vi.fn<(pid: number) => Promise<void>>());
+vi.mock("../utils/processTree.js", async (importOriginal) => ({
+  ...(await importOriginal<typeof import("../utils/processTree.js")>()),
+  terminateWindowsProcessTree: treeKill,
+}));
+
+afterEach(() => {
+  treeKill.mockReset();
+  vi.restoreAllMocks();
+});
+
 it("kills a browser that acknowledged close but never exits, so every caller's close() returns", async () => {
   const child = spawn(process.execPath, ["-e", "setTimeout(() => {}, 60000)"], { stdio: "pipe" });
   const browser = { process: () => child, close: () => once(child, "exit") } as unknown as Browser;
@@ -18,3 +29,24 @@ it("kills a browser that acknowledged close but never exits, so every caller's c
     child.kill("SIGKILL");
   }
 });
+
+it("on Windows ends the browser's whole tree while its root still lives, since children outlive a killed root", async () => {
+  vi.spyOn(process, "platform", "get").mockReturnValue("win32");
+  const child = spawn(process.execPath, ["-e", "setTimeout(() => {}, 60000)"], { stdio: "pipe" });
+  let rootAliveAtTreeKill: boolean | undefined;
+  treeKill.mockImplementation(async () => {
+    rootAliveAtTreeKill = child.exitCode === null && child.signalCode === null;
+  });
+  const browser = { process: () => child, close: () => once(child, "exit") } as unknown as Browser;
+  const puppeteer = {
+    launch: async (_options: LaunchOptions) => browser,
+  } as unknown as PuppeteerNode;
+  try {
+    const launched = await launchManagedBrowser(puppeteer, { headless: true }, { diagnose: false });
+    await launched.close();
+    expect(treeKill).toHaveBeenCalledWith(child.pid);
+    expect(rootAliveAtTreeKill).toBe(true);
+  } finally {
+    child.kill("SIGKILL");
+  }
+});
diff --git a/packages/cli/src/browser/launch.ts b/packages/cli/src/browser/launch.ts
index db2d3799aa..84b7e362aa 100644
--- a/packages/cli/src/browser/launch.ts
+++ b/packages/cli/src/browser/launch.ts
@@ -17,7 +17,7 @@ import {
 } from "./gpuPolicy.js";
 import { normalizeErrorMessage, notePageCrash } from "../utils/errorMessage.js";
 import { requestCliExit } from "../utils/commandResult.js";
-import { processIsAlive } from "../utils/processTree.js";
+import { processIsAlive, terminateWindowsProcessTree } from "../utils/processTree.js";
 import { chromeDescendants, reapChromeTree } from "./chromeTree.js";
 import { watchChromeTree, type ChromeWatchdog } from "./windowsChromeWatchdog.js";
 
@@ -290,6 +290,13 @@ function closeGracefully(browser: Browser): Promise<void> {
   return (gracefulClose.get(browser) ?? (() => browser.close()))();
 }
 
+async function killBrowser(child: ChildProcess): Promise<void> {
+  if (process.platform === "win32" && child.pid !== undefined) {
+    await terminateWindowsProcessTree(child.pid).catch(() => undefined);
+  }
+  child.kill("SIGKILL");
+}
+
 async function closedWithoutKill(browser: Browser): Promise<boolean> {
   const child = browser.process();
   if (!child) throw new Error("A managed browser lost its owned process.");
@@ -309,7 +316,7 @@ async function closedWithoutKill(browser: Browser): Promise<boolean> {
       grace,
     ]);
     const clean = child.exitCode !== null || child.signalCode !== null;
-    if (!clean) child.kill("SIGKILL");
+    if (!clean) await killBrowser(child);
     clearTimeout(timer);
     const exitLimit = new Promise<never>((_, reject) => {
       timer = setTimeout(