diff --git a/packages/browser/src/helpers/isValidDomain.test.ts b/packages/browser/src/helpers/isValidDomain.test.ts
new file mode 100644
index 00000000..389e14b1
--- /dev/null
+++ b/packages/browser/src/helpers/isValidDomain.test.ts
@@ -0,0 +1,26 @@
+import { assert, assertFalse } from '@std/assert';
+import { isValidDomain } from './isValidDomain.ts';
+
+Deno.test('should handle localhost', () => {
+  assert(isValidDomain('localhost'));
+});
+
+Deno.test('should handle standard ASCII domains and labels', () => {
+  assert(isValidDomain('example.com'));
+  assert(isValidDomain('my-site.io'));
+  assert(isValidDomain('sub.example.co.uk'));
+  assertFalse(isValidDomain('notadomain'));
+  assertFalse(isValidDomain(''));
+});
+
+Deno.test('should handle punycode domains', () => {
+  // Punycode label with ascii domain
+  assert(isValidDomain('xn--5lwo46cp2i.co.jp'));
+  assert(isValidDomain('xn--5lwo46cp2i.jp'));
+  // Punycode label with punycode domain
+  assert(isValidDomain('xn--80akjhbed8ahk.xn--p1ai'));
+  // ASCII subdomain
+  assert(isValidDomain('login.xn--5lwo46cp2i.co.jp'));
+  // Punycode subdomain
+  assert(isValidDomain('xn--sub.xn--5lwo46cp2i.co.jp'));
+});
diff --git a/packages/browser/src/helpers/isValidDomain.ts b/packages/browser/src/helpers/isValidDomain.ts
index 22f045fd..3b03eee5 100644
--- a/packages/browser/src/helpers/isValidDomain.ts
+++ b/packages/browser/src/helpers/isValidDomain.ts
@@ -3,13 +3,14 @@
  *
  * A "valid domain" is defined here: https://url.spec.whatwg.org/#valid-domain
  *
- * Regex sourced from here:
+ * Regex was originally sourced from here, then remixed to add punycode support:
  * https://www.oreilly.com/library/view/regular-expressions-cookbook/9781449327453/ch08s15.html
  */
 export function isValidDomain(hostname: string): boolean {
   return (
     // Consider localhost valid as well since it's okay wrt Secure Contexts
     hostname === 'localhost' ||
-    /^([a-z0-9]+(-[a-z0-9]+)*\.)+[a-z]{2,}$/i.test(hostname)
+    // Support punycode (ACE) or ascii labels and domains
+    /^((xn--[a-z0-9-]+|[a-z0-9]+(-[a-z0-9]+)*)\.)+([a-z]{2,}|xn--[a-z0-9-]+)$/i.test(hostname)
   );
 }