diff --git a/lib/sender.js b/lib/sender.js
index c84885362..1ed04b027 100644
--- a/lib/sender.js
+++ b/lib/sender.js
@@ -1,9 +1,8 @@
-/* eslint no-unused-vars: ["error", { "varsIgnorePattern": "^net|tls$" }] */
+/* eslint no-unused-vars: ["error", { "varsIgnorePattern": "^Duplex" }] */
 
 'use strict';
 
-const net = require('net');
-const tls = require('tls');
+const { Duplex } = require('stream');
 const { randomFillSync } = require('crypto');
 
 const PerMessageDeflate = require('./permessage-deflate');
@@ -21,7 +20,7 @@ class Sender {
   /**
    * Creates a Sender instance.
    *
-   * @param {(net.Socket|tls.Socket)} socket The connection socket
+   * @param {Duplex} socket The connection socket
    * @param {Object} [extensions] An object containing the negotiated extensions
    * @param {Function} [generateMask] The function used to generate the masking
    *     key
diff --git a/lib/websocket-server.js b/lib/websocket-server.js
index bac30eb33..b0ed7bd2e 100644
--- a/lib/websocket-server.js
+++ b/lib/websocket-server.js
@@ -1,12 +1,10 @@
-/* eslint no-unused-vars: ["error", { "varsIgnorePattern": "^net|tls|https$" }] */
+/* eslint no-unused-vars: ["error", { "varsIgnorePattern": "^Duplex$" }] */
 
 'use strict';
 
 const EventEmitter = require('events');
 const http = require('http');
-const https = require('https');
-const net = require('net');
-const tls = require('tls');
+const { Duplex } = require('stream');
 const { createHash } = require('crypto');
 
 const extension = require('./extension');
@@ -221,8 +219,7 @@ class WebSocketServer extends EventEmitter {
    * Handle a HTTP Upgrade request.
    *
    * @param {http.IncomingMessage} req The request object
-   * @param {(net.Socket|tls.Socket)} socket The network socket between the
-   *     server and client
+   * @param {Duplex} socket The network socket between the server and client
    * @param {Buffer} head The first packet of the upgraded stream
    * @param {Function} cb Callback
    * @public
@@ -346,8 +343,7 @@ class WebSocketServer extends EventEmitter {
    * @param {String} key The value of the `Sec-WebSocket-Key` header
    * @param {Set} protocols The subprotocols
    * @param {http.IncomingMessage} req The request object
-   * @param {(net.Socket|tls.Socket)} socket The network socket between the
-   *     server and client
+   * @param {Duplex} socket The network socket between the server and client
    * @param {Buffer} head The first packet of the upgraded stream
    * @param {Function} cb Callback
    * @throws {Error} If called more than once with the same socket
@@ -477,7 +473,7 @@ function socketOnError() {
 /**
  * Close the connection when preconditions are not fulfilled.
  *
- * @param {(net.Socket|tls.Socket)} socket The socket of the upgrade request
+ * @param {Duplex} socket The socket of the upgrade request
  * @param {Number} code The HTTP response status code
  * @param {String} [message] The HTTP response body
  * @param {Object} [headers] Additional HTTP response headers
@@ -518,7 +514,7 @@ function abortHandshake(socket, code, message, headers) {
  *
  * @param {WebSocketServer} server The WebSocket server
  * @param {http.IncomingMessage} req The request object
- * @param {(net.Socket|tls.Socket)} socket The socket of the upgrade request
+ * @param {Duplex} socket The socket of the upgrade request
  * @param {Number} code The HTTP response status code
  * @param {String} message The HTTP response body
  * @private
diff --git a/lib/websocket.js b/lib/websocket.js
index 15f61acee..8685ff73a 100644
--- a/lib/websocket.js
+++ b/lib/websocket.js
@@ -1,4 +1,4 @@
-/* eslint no-unused-vars: ["error", { "varsIgnorePattern": "^Readable$" }] */
+/* eslint no-unused-vars: ["error", { "varsIgnorePattern": "^Duplex|Readable$" }] */
 
 'use strict';
 
@@ -8,7 +8,7 @@ const http = require('http');
 const net = require('net');
 const tls = require('tls');
 const { randomBytes, createHash } = require('crypto');
-const { Readable } = require('stream');
+const { Duplex, Readable } = require('stream');
 const { URL } = require('url');
 
 const PerMessageDeflate = require('./permessage-deflate');
@@ -189,8 +189,7 @@ class WebSocket extends EventEmitter {
   /**
    * Set up the socket and the internal resources.
    *
-   * @param {(net.Socket|tls.Socket)} socket The network socket between the
-   *     server and client
+   * @param {Duplex} socket The network socket between the server and client
    * @param {Buffer} head The first packet of the upgraded stream
    * @param {Object} options Options object
    * @param {Function} [options.generateMask] The function used to generate the
@@ -223,13 +222,11 @@ class WebSocket extends EventEmitter {
     receiver.on('ping', receiverOnPing);
     receiver.on('pong', receiverOnPong);
 
-    // These methods may not be available if `socket` is actually just a stream:
-    if (socket.setTimeout) {
-      socket.setTimeout(0);
-    }
-    if (socket.setNoDelay) {
-      socket.setNoDelay();
-    }
+    //
+    // These methods may not be available if `socket` is just a `Duplex`.
+    //
+    if (socket.setTimeout) socket.setTimeout(0);
+    if (socket.setNoDelay) socket.setNoDelay();
 
     if (head.length > 0) socket.unshift(head);
 
@@ -1229,7 +1226,7 @@ function resume(stream) {
 }
 
 /**
- * The listener of the `net.Socket` `'close'` event.
+ * The listener of the socket `'close'` event.
  *
  * @private
  */
@@ -1280,7 +1277,7 @@ function socketOnClose() {
 }
 
 /**
- * The listener of the `net.Socket` `'data'` event.
+ * The listener of the socket `'data'` event.
  *
  * @param {Buffer} chunk A chunk of data
  * @private
@@ -1292,7 +1289,7 @@ function socketOnData(chunk) {
 }
 
 /**
- * The listener of the `net.Socket` `'end'` event.
+ * The listener of the socket `'end'` event.
  *
  * @private
  */
@@ -1305,7 +1302,7 @@ function socketOnEnd() {
 }
 
 /**
- * The listener of the `net.Socket` `'error'` event.
+ * The listener of the socket `'error'` event.
  *
  * @private
  */
diff --git a/test/websocket-server.test.js b/test/websocket-server.test.js
index 33d7a65f8..b962edcb9 100644
--- a/test/websocket-server.test.js
+++ b/test/websocket-server.test.js
@@ -516,19 +516,24 @@ describe('WebSocketServer', () => {
       });
     });
 
-    it('can complete a WebSocket upgrade over any duplex stream', (done) => {
+    it('completes a WebSocket upgrade over any duplex stream', (done) => {
       const server = http.createServer();
 
       server.listen(0, () => {
         const wss = new WebSocket.Server({ noServer: true });
 
         server.on('upgrade', (req, socket, head) => {
-          // Put a stream between the raw socket and our websocket processing:
+          //
+          // Put a stream between the raw socket and our websocket processing.
+          //
           const { socket1: stream1, socket2: stream2 } = new DuplexPair();
+
           socket.pipe(stream1);
           stream1.pipe(socket);
 
-          // Pass the other side of the stream as the socket to upgrade:
+          //
+          // Pass the other side of the stream as the socket to upgrade.
+          //
           wss.handleUpgrade(req, stream2, head, (ws) => {
             ws.send('hello');
             ws.close();