diff --git a/lib/internal/navigator.js b/lib/internal/navigator.js
index 2904779a47e64b..64e9600167f050 100644
--- a/lib/internal/navigator.js
+++ b/lib/internal/navigator.js
@@ -11,6 +11,7 @@ const {
 
 const {
   ERR_ILLEGAL_CONSTRUCTOR,
+  ERR_INVALID_THIS,
 } = require('internal/errors').codes;
 
 const {
@@ -79,7 +80,8 @@ function getNavigatorPlatform(arch, platform) {
 }
 
 class Navigator {
-  // Private properties are used to avoid brand validations.
+  // Private properties are used to avoid brand validations: reading a private
+  // field from a non-Navigator receiver throws a TypeError on its own.
   #availableParallelism;
   #locks;
   #userAgent;
@@ -113,6 +115,10 @@ class Navigator {
    * @returns {string}
    */
   get language() {
+    // `language` does not read a private field, so brand-check explicitly
+    // to keep parity with the other getters when called on a non-Navigator
+    // receiver (e.g. `Navigator.prototype.language`).
+    if (!(#languages in this)) throw new ERR_INVALID_THIS('Navigator');
     // The default locale might be changed dynamically, so always invoke the
     // binding.
     return getDefaultLocale() || 'en-US';
diff --git a/test/parallel/test-navigator.js b/test/parallel/test-navigator.js
index 01c5595b93cd12..82e3fe903d455f 100644
--- a/test/parallel/test-navigator.js
+++ b/test/parallel/test-navigator.js
@@ -147,3 +147,19 @@ Object.defineProperty(navigator, 'language', { value: 'for-testing' });
 assert.strictEqual(navigator.language, 'for-testing');
 assert.strictEqual(navigator.languages.length, 1);
 assert.strictEqual(navigator.languages[0] !== 'for-testing', true);
+
+{
+  const { Navigator } = globalThis;
+  for (const name of Object.keys(Navigator.prototype)) {
+    assert.throws(
+      () => Navigator.prototype[name],
+      { name: 'TypeError' },
+      `expected TypeError when reading ${name} on Navigator.prototype`,
+    );
+    assert.throws(
+      () => Reflect.get(Navigator.prototype, name, {}),
+      { name: 'TypeError' },
+      `expected TypeError when reading ${name} on a plain object`,
+    );
+  }
+}