diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8cf4926..75bf22a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -18,7 +18,10 @@ jobs:
       matrix:
         node-version: [16.x, 18.x, 20.x, 21.x, 22.x]
         # See supported Node.js release schedule at https://nodejs.org/en/about/releases/
-        os: [macos-latest, ubuntu-latest, windows-latest]
+        os:
+          - macos-latest
+          - ubuntu-latest
+          - windows-latest
 
     steps:
     - uses: actions/checkout@v3
diff --git a/.mocharc.yml b/.mocharc.yml
index f8726ea..f945fba 100644
--- a/.mocharc.yml
+++ b/.mocharc.yml
@@ -1,3 +1,4 @@
 timeout: 4000
 require:
   - ts-node/register
+full-trace: true
diff --git a/README.md b/README.md
index 23348fc..91f96a6 100644
--- a/README.md
+++ b/README.md
@@ -51,21 +51,23 @@ npm install kill-port-process -g
 
 You can use the CLI calling it with `kill-port <port>`.
 
-It takes a single port or a list of ports separated by a space. Valid flags are `-p` and `--port` but are both optional.
-
 ```bash
+# single port
 $ kill-port 1234
-# or multiple ports, separated by space(s)
+# multiple ports, separated by space(s)
 $ kill-port 1234 2345
-# or
+# with "-p" flag
 $ kill-port -p 1234
-# or
+# with with "--port" flag
 $ kill-port --port 1234
+# with graceful flag
+$ kill-port 1234 --graceful
 ```
 
 #### Flags
 
-* `--graceful` kill the process gracefully.
+* `-p` or `--port` (optional): used to specify the port(s) to kill. Takes a single port or a list of ports separated by a space.
+* `--graceful` (optional) kill the process gracefully.
   * **Unix:** Sends a `-15` signal to kill (`SIGTERM`) rather than `-9` (`SIGKILL`)
   * **Win:** Currently no use
 
diff --git a/package-lock.json b/package-lock.json
index 67a4e23..6b88800 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
 	"name": "kill-port-process",
-	"version": "3.2.1",
+	"version": "4.0.0-beta.0",
 	"lockfileVersion": 3,
 	"requires": true,
 	"packages": {
 		"": {
 			"name": "kill-port-process",
-			"version": "3.2.1",
+			"version": "4.0.0-beta.0",
 			"license": "ISC",
 			"dependencies": {
 				"get-them-args": "1.3.2",
diff --git a/package.json b/package.json
index 8bd8387..72de3d6 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
 	"name": "kill-port-process",
-	"version": "3.2.1",
+	"version": "4.0.0-beta.0",
 	"description": "Easily kill hanging processes on ports - on any platform!",
 	"main": "dist/lib/index.js",
 	"bin": {
@@ -11,11 +11,11 @@
 		"build": "tsc",
 		"eslint": "eslint . --ext .ts",
 		"lint": "npm run eslint",
+		"git-tags": "git push && git push --tags",
 		"test": "mocha test/*.spec.ts",
 		"pretest": "npm run build",
 		"prepare": "npm run build && npm test",
-		"preversion": "npm run build && npm test",
-		"postversion": "git push && git push --tags"
+		"preversion": "npm run build && npm test"
 	},
 	"keywords": [
 		"process",
diff --git a/src/bin/kill-port-process.ts b/src/bin/kill-port-process.ts
index 4fa9085..05d1bc4 100644
--- a/src/bin/kill-port-process.ts
+++ b/src/bin/kill-port-process.ts
@@ -21,6 +21,9 @@ import { killPortProcess, Options } from '../lib/index';
 	const flags = parseFlagsFromArgs(args);
 	const options = formatOptions(flags);
 
+	console.log('flags::', flags);
+	console.log('options::', options);
+
 	await killPortProcess(ports, options);
 })();
 
diff --git a/src/lib/killer.ts b/src/lib/killer.ts
index addcadd..5b6bd50 100644
--- a/src/lib/killer.ts
+++ b/src/lib/killer.ts
@@ -9,7 +9,7 @@ type KillOptions = {
 }
 
 export class Killer {
-	protected ports: number[];
+	private readonly ports: number[];
 
 	constructor(ports: number[]) {
 		this.ports = ports;
@@ -17,12 +17,13 @@ export class Killer {
 
 	public async kill(options: KillOptions) {
 		const killFunc = platform() === 'win32' ? this.win32Kill : this.unixKill;
+
 		const promises = this.ports.map((port) => killFunc(port, options.signal));
 
 		return Promise.all(promises);
 	}
 
-	private async win32Kill(port: number, signal: Signal) {
+	private async win32Kill(port: number) {
 		const pid = await pidFromPort(port).catch((error) => console.error('Failed to get pid of port', port, error));
 
 		if (!pid) {
@@ -67,14 +68,32 @@ export class Killer {
 
 			xargs.stdout.pipe(process.stdin);
 			xargs.stderr.on('data', logStderrData('xargs'));
-			xargs.on('close', (code) => {
-				if (code !== 0) {
-					return reject();
+
+			xargs.on('exit', (code) => {
+				const error = handleErrorCode(code);
+				if (error) {
+					reject(error);
 				}
 
 				resolve(undefined);
 			});
 
+			/**
+			 * @see https://www.commandlinux.com/man-page/man1/xargs.1.html for possible exit codes
+			 */
+			function handleErrorCode(code: number | null) {
+				if (!code) {
+					return null;
+				}
+
+				switch (code) {
+					case 1:
+						return new Error(`xargs process exited with code ${code}`)
+					case 127:
+						return new Error('xargs command not found');
+				}
+			}
+
 			function logStderrData(command: string) {
 				return (data: any) => console.error(`${command} - ${data.toString()}`);
 			}