diff --git a/lib/websocket-server.js b/lib/websocket-server.js
index d0a29783f..059b0a572 100644
--- a/lib/websocket-server.js
+++ b/lib/websocket-server.js
@@ -230,21 +230,34 @@ class WebSocketServer extends EventEmitter {
   handleUpgrade(req, socket, head, cb) {
     socket.on('error', socketOnError);
 
-    const key =
-      req.headers['sec-websocket-key'] !== undefined
-        ? req.headers['sec-websocket-key']
-        : false;
+    const key = req.headers['sec-websocket-key'];
     const version = +req.headers['sec-websocket-version'];
 
-    if (
-      req.method !== 'GET' ||
-      req.headers.upgrade.toLowerCase() !== 'websocket' ||
-      !key ||
-      !keyRegex.test(key) ||
-      (version !== 8 && version !== 13) ||
-      !this.shouldHandle(req)
-    ) {
-      return abortHandshake(socket, 400);
+    if (req.method !== 'GET') {
+      abortHandshake(socket, 405, 'The HTTP method is invalid');
+      return;
+    }
+
+    if (req.headers.upgrade.toLowerCase() !== 'websocket') {
+      abortHandshake(socket, 400, 'The Upgrade header is invalid');
+      return;
+    }
+
+    if (!key || !keyRegex.test(key)) {
+      const message = 'The Sec-WebSocket-Key header is missing or invalid';
+      abortHandshake(socket, 400, message);
+      return;
+    }
+
+    if (version !== 8 && version !== 13) {
+      const message = 'The Sec-WebSocket-Version header is missing or invalid';
+      abortHandshake(socket, 400, message);
+      return;
+    }
+
+    if (!this.shouldHandle(req)) {
+      abortHandshake(socket, 400);
+      return;
     }
 
     const secWebSocketProtocol = req.headers['sec-websocket-protocol'];
@@ -254,7 +267,9 @@ class WebSocketServer extends EventEmitter {
       try {
         protocols = subprotocol.parse(secWebSocketProtocol);
       } catch (err) {
-        return abortHandshake(socket, 400);
+        const message = 'The Sec-WebSocket-Protocol header is invalid';
+        abortHandshake(socket, 400, message);
+        return;
       }
     }
 
@@ -279,7 +294,10 @@ class WebSocketServer extends EventEmitter {
           extensions[PerMessageDeflate.extensionName] = perMessageDeflate;
         }
       } catch (err) {
-        return abortHandshake(socket, 400);
+        const message =
+          'The Sec-WebSocket-Extensions header is invalid or not acceptable';
+        abortHandshake(socket, 400, message);
+        return;
       }
     }
 
@@ -446,7 +464,7 @@ function emitClose(server) {
 }
 
 /**
- * Handle premature socket errors.
+ * Handle socket errors.
  *
  * @private
  */
@@ -464,25 +482,30 @@ function socketOnError() {
  * @private
  */
 function abortHandshake(socket, code, message, headers) {
-  if (socket.writable) {
-    message = message || http.STATUS_CODES[code];
-    headers = {
-      Connection: 'close',
-      'Content-Type': 'text/html',
-      'Content-Length': Buffer.byteLength(message),
-      ...headers
-    };
+  //
+  // The socket is writable unless the user destroyed or ended it before calling
+  // `server.handleUpgrade()` or in the `verifyClient` function, which is a user
+  // error. Handling this does not make much sense as the worst that can happen
+  // is that some of the data written by the user might be discarded due to the
+  // call to `socket.end()` below, which triggers an `'error'` event that in
+  // turn causes the socket to be destroyed.
+  //
+  message = message || http.STATUS_CODES[code];
+  headers = {
+    Connection: 'close',
+    'Content-Type': 'text/html',
+    'Content-Length': Buffer.byteLength(message),
+    ...headers
+  };
 
-    socket.write(
-      `HTTP/1.1 ${code} ${http.STATUS_CODES[code]}\r\n` +
-        Object.keys(headers)
-          .map((h) => `${h}: ${headers[h]}`)
-          .join('\r\n') +
-        '\r\n\r\n' +
-        message
-    );
-  }
+  socket.once('finish', socket.destroy);
 
-  socket.removeListener('error', socketOnError);
-  socket.destroy();
+  socket.end(
+    `HTTP/1.1 ${code} ${http.STATUS_CODES[code]}\r\n` +
+      Object.keys(headers)
+        .map((h) => `${h}: ${headers[h]}`)
+        .join('\r\n') +
+      '\r\n\r\n' +
+      message
+  );
 }
diff --git a/test/websocket-server.test.js b/test/websocket-server.test.js
index fd494059f..5590d6c99 100644
--- a/test/websocket-server.test.js
+++ b/test/websocket-server.test.js
@@ -470,7 +470,9 @@ describe('WebSocketServer', () => {
           port: wss.address().port,
           headers: {
             Connection: 'Upgrade',
-            Upgrade: 'websocket'
+            Upgrade: 'websocket',
+            'Sec-WebSocket-Key': 'dGhlIHNhbXBsZSBub25jZQ==',
+            'Sec-WebSocket-Version': 13
           }
         });
 
@@ -496,7 +498,20 @@ describe('WebSocketServer', () => {
 
         req.on('response', (res) => {
           assert.strictEqual(res.statusCode, 400);
-          wss.close(done);
+
+          const chunks = [];
+
+          res.on('data', (chunk) => {
+            chunks.push(chunk);
+          });
+
+          res.on('end', () => {
+            assert.strictEqual(
+              Buffer.concat(chunks).toString(),
+              'The Sec-WebSocket-Key header is missing or invalid'
+            );
+            wss.close(done);
+          });
         });
       });
     });
@@ -539,6 +554,77 @@ describe('WebSocketServer', () => {
   });
 
   describe('Connection establishing', () => {
+    it('fails if the HTTP method is not GET', (done) => {
+      const wss = new WebSocket.Server({ port: 0 }, () => {
+        const req = http.request({
+          method: 'POST',
+          port: wss.address().port,
+          headers: {
+            Connection: 'Upgrade',
+            Upgrade: 'websocket'
+          }
+        });
+
+        req.on('response', (res) => {
+          assert.strictEqual(res.statusCode, 405);
+
+          const chunks = [];
+
+          res.on('data', (chunk) => {
+            chunks.push(chunk);
+          });
+
+          res.on('end', () => {
+            assert.strictEqual(
+              Buffer.concat(chunks).toString(),
+              'The HTTP method is invalid'
+            );
+            wss.close(done);
+          });
+        });
+
+        req.end();
+      });
+
+      wss.on('connection', () => {
+        done(new Error("Unexpected 'connection' event"));
+      });
+    });
+
+    it('fails if the Upgrade header field value is not "websocket"', (done) => {
+      const wss = new WebSocket.Server({ port: 0 }, () => {
+        const req = http.get({
+          port: wss.address().port,
+          headers: {
+            Connection: 'Upgrade',
+            Upgrade: 'foo'
+          }
+        });
+
+        req.on('response', (res) => {
+          assert.strictEqual(res.statusCode, 400);
+
+          const chunks = [];
+
+          res.on('data', (chunk) => {
+            chunks.push(chunk);
+          });
+
+          res.on('end', () => {
+            assert.strictEqual(
+              Buffer.concat(chunks).toString(),
+              'The Upgrade header is invalid'
+            );
+            wss.close(done);
+          });
+        });
+      });
+
+      wss.on('connection', () => {
+        done(new Error("Unexpected 'connection' event"));
+      });
+    });
+
     it('fails if the Sec-WebSocket-Key header is invalid (1/2)', (done) => {
       const wss = new WebSocket.Server({ port: 0 }, () => {
         const req = http.get({
@@ -551,7 +637,20 @@ describe('WebSocketServer', () => {
 
         req.on('response', (res) => {
           assert.strictEqual(res.statusCode, 400);
-          wss.close(done);
+
+          const chunks = [];
+
+          res.on('data', (chunk) => {
+            chunks.push(chunk);
+          });
+
+          res.on('end', () => {
+            assert.strictEqual(
+              Buffer.concat(chunks).toString(),
+              'The Sec-WebSocket-Key header is missing or invalid'
+            );
+            wss.close(done);
+          });
         });
       });
 
@@ -573,7 +672,20 @@ describe('WebSocketServer', () => {
 
         req.on('response', (res) => {
           assert.strictEqual(res.statusCode, 400);
-          wss.close(done);
+
+          const chunks = [];
+
+          res.on('data', (chunk) => {
+            chunks.push(chunk);
+          });
+
+          res.on('end', () => {
+            assert.strictEqual(
+              Buffer.concat(chunks).toString(),
+              'The Sec-WebSocket-Key header is missing or invalid'
+            );
+            wss.close(done);
+          });
         });
       });
 
@@ -595,7 +707,20 @@ describe('WebSocketServer', () => {
 
         req.on('response', (res) => {
           assert.strictEqual(res.statusCode, 400);
-          wss.close(done);
+
+          const chunks = [];
+
+          res.on('data', (chunk) => {
+            chunks.push(chunk);
+          });
+
+          res.on('end', () => {
+            assert.strictEqual(
+              Buffer.concat(chunks).toString(),
+              'The Sec-WebSocket-Version header is missing or invalid'
+            );
+            wss.close(done);
+          });
         });
       });
 
@@ -618,7 +743,20 @@ describe('WebSocketServer', () => {
 
         req.on('response', (res) => {
           assert.strictEqual(res.statusCode, 400);
-          wss.close(done);
+
+          const chunks = [];
+
+          res.on('data', (chunk) => {
+            chunks.push(chunk);
+          });
+
+          res.on('end', () => {
+            assert.strictEqual(
+              Buffer.concat(chunks).toString(),
+              'The Sec-WebSocket-Version header is missing or invalid'
+            );
+            wss.close(done);
+          });
         });
       });
 
@@ -642,7 +780,20 @@ describe('WebSocketServer', () => {
 
         req.on('response', (res) => {
           assert.strictEqual(res.statusCode, 400);
-          wss.close(done);
+
+          const chunks = [];
+
+          res.on('data', (chunk) => {
+            chunks.push(chunk);
+          });
+
+          res.on('end', () => {
+            assert.strictEqual(
+              Buffer.concat(chunks).toString(),
+              'The Sec-WebSocket-Protocol header is invalid'
+            );
+            wss.close(done);
+          });
         });
       });
 
@@ -672,7 +823,21 @@ describe('WebSocketServer', () => {
 
           req.on('response', (res) => {
             assert.strictEqual(res.statusCode, 400);
-            wss.close(done);
+
+            const chunks = [];
+
+            res.on('data', (chunk) => {
+              chunks.push(chunk);
+            });
+
+            res.on('end', () => {
+              assert.strictEqual(
+                Buffer.concat(chunks).toString(),
+                'The Sec-WebSocket-Extensions header is invalid or not ' +
+                  'acceptable'
+              );
+              wss.close(done);
+            });
           });
         }
       );