diff --git a/scripts/lib/managed-child-process.mjs b/scripts/lib/managed-child-process.mjs
index 9bbf8e3896e..63720614f78 100644
--- a/scripts/lib/managed-child-process.mjs
+++ b/scripts/lib/managed-child-process.mjs
@@ -48,6 +48,7 @@ export function terminateManagedChild(child, signal = "SIGTERM") {
  *   env?: NodeJS.ProcessEnv;
  *   stdio?: import("node:child_process").StdioOptions;
  *   shell?: boolean;
+ *   onReady?: (child: import("node:child_process").ChildProcess) => void;
  * }} options
  * @returns {Promise<number>}
  */
@@ -58,6 +59,7 @@ export async function runManagedCommand({
   env,
   stdio = "inherit",
   shell = process.platform === "win32",
+  onReady,
 }) {
   const child = spawn(bin, args, {
     cwd,
@@ -81,6 +83,7 @@ export async function runManagedCommand({
   for (const signal of FORWARDED_SIGNALS) {
     process.once(signal, forwardSignal);
   }
+  onReady?.(child);
 
   try {
     return await new Promise((resolve, reject) => {
diff --git a/test/scripts/managed-child-process.test.ts b/test/scripts/managed-child-process.test.ts
index 0759cb86c19..237c17a1a95 100644
--- a/test/scripts/managed-child-process.test.ts
+++ b/test/scripts/managed-child-process.test.ts
@@ -21,6 +21,7 @@ describe("managed-child-process", () => {
     const childPath = path.join(dir, "child.mjs");
     const runnerPath = path.join(dir, "runner.mjs");
     const childPidPath = path.join(dir, "child.pid");
+    const runnerReadyPath = path.join(dir, "runner.ready");
     const helperUrl = pathToFileURL(path.resolve("scripts/lib/managed-child-process.mjs")).href;
 
     fs.writeFileSync(
@@ -39,12 +40,14 @@ setInterval(() => {}, 1_000);
     fs.writeFileSync(
       runnerPath,
       `
+import fs from "node:fs";
 import { runManagedCommand } from ${JSON.stringify(helperUrl)};
 
 process.exitCode = await runManagedCommand({
   bin: process.execPath,
   args: [${JSON.stringify(childPath)}, ${JSON.stringify(childPidPath)}],
   stdio: "ignore",
+  onReady: () => fs.writeFileSync(${JSON.stringify(runnerReadyPath)}, "1"),
 });
 `,
       "utf8",
@@ -56,6 +59,7 @@ process.exitCode = await runManagedCommand({
     let childPid = 0;
 
     try {
+      await waitFor(() => fs.existsSync(runnerReadyPath));
       await waitFor(() => fs.existsSync(childPidPath));
       childPid = Number(fs.readFileSync(childPidPath, "utf8"));
       expect(Number.isInteger(childPid)).toBe(true);