diff --git a/packages/kbn-optimizer/package.json b/packages/kbn-optimizer/package.json
index b7c9a63897bf9..7bd7a236a43aa 100644
--- a/packages/kbn-optimizer/package.json
+++ b/packages/kbn-optimizer/package.json
@@ -28,6 +28,7 @@
     "cpy": "^8.0.0",
     "css-loader": "^3.4.2",
     "del": "^5.1.0",
+    "execa": "^4.0.2",
     "file-loader": "^4.2.0",
     "istanbul-instrumenter-loader": "^3.0.1",
     "jest-diff": "^25.1.0",
diff --git a/packages/kbn-optimizer/src/optimizer/observe_worker.ts b/packages/kbn-optimizer/src/optimizer/observe_worker.ts
index f5c944cefb76f..c929cf62d1bb0 100644
--- a/packages/kbn-optimizer/src/optimizer/observe_worker.ts
+++ b/packages/kbn-optimizer/src/optimizer/observe_worker.ts
@@ -17,10 +17,10 @@
  * under the License.
  */
 
-import { fork, ChildProcess } from 'child_process';
 import { Readable } from 'stream';
 import { inspect } from 'util';
 
+import execa from 'execa';
 import * as Rx from 'rxjs';
 import { map, takeUntil } from 'rxjs/operators';
 
@@ -42,7 +42,7 @@ export interface WorkerStarted {
 export type WorkerStatus = WorkerStdio | WorkerStarted;
 
 interface ProcResource extends Rx.Unsubscribable {
-  proc: ChildProcess;
+  proc: execa.ExecaChildProcess;
 }
 const isNumeric = (input: any) => String(input).match(/^[0-9]+$/);
 
@@ -70,20 +70,22 @@ function usingWorkerProc<T>(
   config: OptimizerConfig,
   workerConfig: WorkerConfig,
   bundles: Bundle[],
-  fn: (proc: ChildProcess) => Rx.Observable<T>
+  fn: (proc: execa.ExecaChildProcess) => Rx.Observable<T>
 ) {
   return Rx.using(
     (): ProcResource => {
       const args = [JSON.stringify(workerConfig), JSON.stringify(bundles.map((b) => b.toSpec()))];
 
-      const proc = fork(require.resolve('../worker/run_worker'), args, {
-        stdio: ['ignore', 'pipe', 'pipe', 'ipc'],
-        execArgv: [
+      const proc = execa.node(require.resolve('../worker/run_worker'), args, {
+        nodeOptions: [
           ...(inspectFlag && config.inspectWorkers
             ? [`${inspectFlag}=${inspectPortCounter++}`]
             : []),
           ...(config.maxWorkerCount <= 3 ? ['--max-old-space-size=2048'] : []),
         ],
+        buffer: false,
+        stderr: 'pipe',
+        stdout: 'pipe',
       });
 
       return {
diff --git a/packages/kbn-pm/dist/index.js b/packages/kbn-pm/dist/index.js
index dab091ddfa9a8..8522f8ed2dc95 100644
--- a/packages/kbn-pm/dist/index.js
+++ b/packages/kbn-pm/dist/index.js
@@ -34812,10 +34812,11 @@ const makeError = ({
 
 	const prefix = getErrorPrefix({timedOut, timeout, errorCode, signal, signalDescription, exitCode, isCanceled});
 	const execaMessage = `Command ${prefix}: ${command}`;
-	const shortMessage = error instanceof Error ? `${execaMessage}\n${error.message}` : execaMessage;
+	const isError = Object.prototype.toString.call(error) === '[object Error]';
+	const shortMessage = isError ? `${execaMessage}\n${error.message}` : execaMessage;
 	const message = [shortMessage, stderr, stdout].filter(Boolean).join('\n');
 
-	if (error instanceof Error) {
+	if (isError) {
 		error.originalMessage = error.message;
 		error.message = message;
 	} else {
@@ -36263,25 +36264,24 @@ module.exports = function (/*streams...*/) {
 
 "use strict";
 
-const mergePromiseProperty = (spawned, promise, property) => {
-	// Starting the main `promise` is deferred to avoid consuming streams
-	const value = typeof promise === 'function' ?
-		(...args) => promise()[property](...args) :
-		promise[property].bind(promise);
 
-	Object.defineProperty(spawned, property, {
-		value,
-		writable: true,
-		enumerable: false,
-		configurable: true
-	});
-};
+const nativePromisePrototype = (async () => {})().constructor.prototype;
+const descriptors = ['then', 'catch', 'finally'].map(property => [
+	property,
+	Reflect.getOwnPropertyDescriptor(nativePromisePrototype, property)
+]);
 
 // The return value is a mixin of `childProcess` and `Promise`
 const mergePromise = (spawned, promise) => {
-	mergePromiseProperty(spawned, promise, 'then');
-	mergePromiseProperty(spawned, promise, 'catch');
-	mergePromiseProperty(spawned, promise, 'finally');
+	for (const [property, descriptor] of descriptors) {
+		// Starting the main `promise` is deferred to avoid consuming streams
+		const value = typeof promise === 'function' ?
+			(...args) => Reflect.apply(descriptor.value, promise(), args) :
+			descriptor.value.bind(promise);
+
+		Reflect.defineProperty(spawned, property, {...descriptor, value});
+	}
+
 	return spawned;
 };
 
diff --git a/yarn.lock b/yarn.lock
index 77cdfa0620c87..b46a219ad7454 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -13042,10 +13042,10 @@ execa@^0.7.0:
     signal-exit "^3.0.0"
     strip-eof "^1.0.0"
 
-execa@^4.0.0:
-  version "4.0.0"
-  resolved "https://registry.yarnpkg.com/execa/-/execa-4.0.0.tgz#7f37d6ec17f09e6b8fc53288611695b6d12b9daf"
-  integrity sha512-JbDUxwV3BoT5ZVXQrSVbAiaXhXUkIwvbhPIwZ0N13kX+5yCzOhUNdocxB/UQRuYOHRYYwAxKYwJYc0T4D12pDA==
+execa@^4.0.0, execa@^4.0.2:
+  version "4.0.2"
+  resolved "https://registry.yarnpkg.com/execa/-/execa-4.0.2.tgz#ad87fb7b2d9d564f70d2b62d511bee41d5cbb240"
+  integrity sha512-QI2zLa6CjGWdiQsmSkZoGtDx2N+cQIGb3yNolGTdjSQzydzLgYYf8LRuagp7S7fPimjcrzUDSUFd/MgzELMi4Q==
   dependencies:
     cross-spawn "^7.0.0"
     get-stream "^5.0.0"