diff --git a/lib/web/websocket/util.js b/lib/web/websocket/util.js
index f9cbf912d09..c60f711cb09 100644
--- a/lib/web/websocket/util.js
+++ b/lib/web/websocket/util.js
@@ -210,8 +210,8 @@ function parseExtensions (extensions) {
     const [name, value = ''] = pair.split('=', 2)
 
     extensionList.set(
-      removeHTTPWhitespace(name, true, false),
-      removeHTTPWhitespace(value, false, true)
+      removeHTTPWhitespace(name, true, true),
+      removeHTTPWhitespace(value, true, true)
     )
 
     position.position++
diff --git a/test/websocket/util.js b/test/websocket/util.js
index b6b05c5ba62..2305e97e794 100644
--- a/test/websocket/util.js
+++ b/test/websocket/util.js
@@ -1,7 +1,7 @@
 'use strict'
 
 const { describe, test } = require('node:test')
-const { isValidSubprotocol } = require('../../lib/web/websocket/util')
+const { isValidSubprotocol, parseExtensions } = require('../../lib/web/websocket/util')
 
 describe('isValidSubprotocol', () => {
   test('empty string returns false', t => {
@@ -28,3 +28,23 @@ describe('isValidSubprotocol', () => {
     }
   })
 })
+
+describe('parseExtensions', () => {
+  test('keeps whitespace out of parameter names and values', t => {
+    // Optional whitespace is allowed around the ";" and "=" delimiters of an
+    // extension header, so it must be stripped from both ends of every name
+    // and value before the map is keyed on them.
+    const cases = {
+      'permessage-deflate; client_max_window_bits': [['permessage-deflate', ''], ['client_max_window_bits', '']],
+      'permessage-deflate ; client_max_window_bits': [['permessage-deflate', ''], ['client_max_window_bits', '']],
+      'permessage-deflate;\tclient_max_window_bits': [['permessage-deflate', ''], ['client_max_window_bits', '']],
+      'permessage-deflate; server_max_window_bits = 10': [['permessage-deflate', ''], ['server_max_window_bits', '10']],
+      'permessage-deflate; server_max_window_bits=10 ': [['permessage-deflate', ''], ['server_max_window_bits', '10']]
+    }
+
+    t.plan(Object.keys(cases).length)
+    for (const [header, expected] of Object.entries(cases)) {
+      t.assert.deepStrictEqual([...parseExtensions(header).entries()], expected, header)
+    }
+  })
+})