diff --git a/.changeset/lovely-phones-kick.md b/.changeset/lovely-phones-kick.md
new file mode 100644
index 00000000..f0216c97
--- /dev/null
+++ b/.changeset/lovely-phones-kick.md
@@ -0,0 +1,8 @@
+---
+'https-proxy-agent': major
+'http-proxy-agent': major
+---
+
+Remove `secureProxy` getter
+
+It was not meant to be a public property. If you were using it, just use `agent.proxy.protocol === 'https:'` instead.
diff --git a/packages/http-proxy-agent/src/index.ts b/packages/http-proxy-agent/src/index.ts
index 7c2a18d9..e373c749 100644
--- a/packages/http-proxy-agent/src/index.ts
+++ b/packages/http-proxy-agent/src/index.ts
@@ -35,10 +35,6 @@ interface HttpProxyAgentClientRequest extends http.ClientRequest {
 	_implicitHeader(): void;
 }
 
-function isHTTPS(protocol?: string | null): boolean {
-	return typeof protocol === 'string' ? /^https:?$/i.test(protocol) : false;
-}
-
 /**
  * The `HttpProxyAgent` implements an HTTP Agent subclass that connects
  * to the specified "HTTP proxy server" in order to proxy HTTP requests.
@@ -50,10 +46,6 @@ export class HttpProxyAgent<Uri extends string> extends Agent {
 	proxyHeaders: OutgoingHttpHeaders | (() => OutgoingHttpHeaders);
 	connectOpts: net.TcpNetConnectOpts & tls.ConnectionOptions;
 
-	get secureProxy() {
-		return isHTTPS(this.proxy.protocol);
-	}
-
 	constructor(proxy: Uri | URL, opts?: HttpProxyAgentOptions<Uri>) {
 		super(opts);
 		this.proxy = typeof proxy === 'string' ? new URL(proxy) : proxy;
@@ -67,7 +59,7 @@ export class HttpProxyAgent<Uri extends string> extends Agent {
 		);
 		const port = this.proxy.port
 			? parseInt(this.proxy.port, 10)
-			: this.secureProxy
+			: this.proxy.protocol === 'https:'
 			? 443
 			: 80;
 		this.connectOpts = {
@@ -159,7 +151,7 @@ export class HttpProxyAgent<Uri extends string> extends Agent {
 
 		// Create a socket connection to the proxy server.
 		let socket: net.Socket;
-		if (this.secureProxy) {
+		if (this.proxy.protocol === 'https:') {
 			debug('Creating `tls.Socket`: %o', this.connectOpts);
 			socket = tls.connect(this.connectOpts);
 		} else {
diff --git a/packages/http-proxy-agent/test/test.ts b/packages/http-proxy-agent/test/test.ts
index 40e74041..77948f69 100644
--- a/packages/http-proxy-agent/test/test.ts
+++ b/packages/http-proxy-agent/test/test.ts
@@ -67,20 +67,6 @@ describe('HttpProxyAgent', () => {
 			const agent = new HttpProxyAgent(proxyUrl);
 			assert.equal(80, agent.defaultPort);
 		});
-		describe('secureProxy', () => {
-			it('should be `false` when "http:" protocol is used', () => {
-				const agent = new HttpProxyAgent(
-					`http://127.0.0.1:${proxyUrl.port}`
-				);
-				assert.equal(false, agent.secureProxy);
-			});
-			it('should be `true` when "https:" protocol is used', () => {
-				const agent = new HttpProxyAgent(
-					`https://127.0.0.1:${proxyUrl.port}`
-				);
-				assert.equal(true, agent.secureProxy);
-			});
-		});
 	});
 
 	describe('"http" module', () => {
diff --git a/packages/https-proxy-agent/src/index.ts b/packages/https-proxy-agent/src/index.ts
index 6bdd9ae5..d136b0c5 100644
--- a/packages/https-proxy-agent/src/index.ts
+++ b/packages/https-proxy-agent/src/index.ts
@@ -47,10 +47,6 @@ export class HttpsProxyAgent<Uri extends string> extends Agent {
 	proxyHeaders: OutgoingHttpHeaders | (() => OutgoingHttpHeaders);
 	connectOpts: net.TcpNetConnectOpts & tls.ConnectionOptions;
 
-	get secureProxy() {
-		return isHTTPS(this.proxy.protocol);
-	}
-
 	constructor(proxy: Uri | URL, opts?: HttpsProxyAgentOptions<Uri>) {
 		super(opts);
 		this.options = { path: undefined };
@@ -65,7 +61,7 @@ export class HttpsProxyAgent<Uri extends string> extends Agent {
 		);
 		const port = this.proxy.port
 			? parseInt(this.proxy.port, 10)
-			: this.secureProxy
+			: this.proxy.protocol === 'https:'
 			? 443
 			: 80;
 		this.connectOpts = {
@@ -85,7 +81,7 @@ export class HttpsProxyAgent<Uri extends string> extends Agent {
 		req: http.ClientRequest,
 		opts: AgentConnectOpts
 	): Promise<net.Socket> {
-		const { proxy, secureProxy } = this;
+		const { proxy } = this;
 
 		if (!opts.host) {
 			throw new TypeError('No "host" provided');
@@ -93,7 +89,7 @@ export class HttpsProxyAgent<Uri extends string> extends Agent {
 
 		// Create a socket connection to the proxy server.
 		let socket: net.Socket;
-		if (secureProxy) {
+		if (proxy.protocol === 'https:') {
 			debug('Creating `tls.Socket`: %o', this.connectOpts);
 			socket = tls.connect(this.connectOpts);
 		} else {
@@ -191,10 +187,6 @@ function resume(socket: net.Socket | tls.TLSSocket): void {
 	socket.resume();
 }
 
-function isHTTPS(protocol?: string | null): boolean {
-	return typeof protocol === 'string' ? /^https:?$/i.test(protocol) : false;
-}
-
 function omit<T extends object, K extends [...(keyof T)[]]>(
 	obj: T,
 	...keys: K
diff --git a/packages/https-proxy-agent/test/test.ts b/packages/https-proxy-agent/test/test.ts
index 0e97c674..992c7610 100644
--- a/packages/https-proxy-agent/test/test.ts
+++ b/packages/https-proxy-agent/test/test.ts
@@ -83,16 +83,6 @@ describe('HttpsProxyAgent', () => {
 			assert.equal(proxyUrl.hostname, agent.proxy.hostname);
 			assert.equal(proxyUrl.port, agent.proxy.port);
 		});
-		describe('secureProxy', () => {
-			it('should be `false` when "http:" protocol is used', () => {
-				const agent = new HttpsProxyAgent(proxyUrl);
-				assert.equal(false, agent.secureProxy);
-			});
-			it('should be `true` when "https:" protocol is used', () => {
-				const agent = new HttpsProxyAgent(sslProxyUrl);
-				assert.equal(true, agent.secureProxy);
-			});
-		});
 	});
 
 	describe('"http" module', () => {