diff -u b/core/lib/Drupal/Component/Utility/UrlHelper.php b/core/lib/Drupal/Component/Utility/UrlHelper.php
--- b/core/lib/Drupal/Component/Utility/UrlHelper.php
+++ b/core/lib/Drupal/Component/Utility/UrlHelper.php
@@ -4,7 +4,6 @@
 
 use Symfony\Component\Validator\Constraints\Url;
 use Symfony\Component\Validator\Constraints\NotBlank;
-use Symfony\Component\Validator\Constraints\NotBlankValidator;
 use Symfony\Component\Validator\Validation;
 
 /**
@@ -398,8 +397,9 @@
    */
   public static function isValid($url, $absolute = FALSE) {
     if ($absolute) {
+      $allowed_protocols = array_unique(array_merge(static::$allowedProtocols, ['http', 'https', 'ftp', 'feed']));
       $violations = Validation::createValidator()->validate($url, [
-        new Url(['protocols' => ['http', 'https', 'ftp', 'feed']]),
+        new Url(['protocols' => $allowed_protocols]),
         new NotBlank(),
       ]);
       return !(bool) count($violations);
diff -u b/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php b/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
--- b/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
+++ b/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
@@ -75,33 +75,7 @@
       // @see https://uasg.tech/
       'ua-test.link',
       'ua-test.technology',
-      // cSpell:disable
-      '普遍接受-测试.top',
-      'ua-test.世界',
-      '普遍接受-测试.世界',
-      '普遍接受-测试.世界',
-      // cSpell:enable
-      // @todo Open dot domains do not validate correctly - they should.
-      // cSpell:disable
-      // '普遍接受-测试。世界',
-      'ua-test.xn--rhqv96g',
-      'xn----f38am99bqvcd5liy1cxsg.top',
-      'xn----f38am99bqvcd5liy1cxsg.xn--rhqv96g',
-      'اختبار-القبولالعالمي.top',
-      'اختبار-القبولالعالمي.شبكة',
-      'ua-test.link/我的页面',
-      'ua-test.technology/我的页面',
-      '普遍接受-测试.top/我的页面',
-      'ua-test.世界/我的页面',
-      '普遍接受-测试.世界/我的页面',
-      // cSpell:enable
-      // @todo Open dot domains do not validate correctly - they should.
-      // '普遍接受-测试。世界/我的页面',
-      // cSpell:disable
-      'ختبار-القبولالعالمي.top/我的页面',
-      'اختبار-القبولالعالمي.شبكة/我的页面',
-      // cSpell:enable
-      'www.example.com/',
+       'www.example.com/',
       // Strings within parenthesis without leading space char.
       'www.example.com/strings_(string_within_parenthesis)',
       // Numbers within parenthesis without leading space char.
@@ -116,10 +90,6 @@
       "foo.com/blah_blah/",
       "foo.com/blah_blah_(wikipedia)",
       "foo.com/blah_blah_(wikipedia)_(again)",
-      // cSpell: disable
-      "www.example.com/wpstyle/?p=364",
-      "www.example.com/foo/?bar=baz&inga=42&quux",
-      // cSpell: enable
       "✪df.ws/123",
       "userid:password@example.com:8080",
       "userid:password@example.com:8080/",
@@ -137,21 +107,39 @@
       // @todo this Url should validation.
       // "foo.com/unicode_(✪)_in_parens",
       "foo.com/(something)?after=parens",
-      // cSpell: disable
-      "☺.damowmow.com/",
-      // cSpell: enable
       "code.google.com/events/#&product=browser",
       "j.mp",
       "foo.bar/baz",
       "foo.bar/?q=Test%20URL-encoded%20stuff",
-      // cSpell: disable
-      "مثال.إختبار",
-      "例子.测试",
-      // cSpell: enable
       // @todo this Url should validation.
       // "-.~_!$&'()*+,;=:%40:80%2f::::::@example.com",
       "1337.net",
       "a.b-c.de",
+      // cSpell: disable
+      '普遍接受-测试.top',
+      'ua-test.世界',
+      '普遍接受-测试.世界',
+      // @todo Open dot domains do not validate correctly - they should.
+      // '普遍接受-测试。世界',
+      // '普遍接受-测试。世界/我的页面',
+      'ua-test.xn--rhqv96g',
+      'xn----f38am99bqvcd5liy1cxsg.top',
+      'xn----f38am99bqvcd5liy1cxsg.xn--rhqv96g',
+      'اختبار-القبولالعالمي.top',
+      'اختبار-القبولالعالمي.شبكة',
+      'ua-test.link/我的页面',
+      'ua-test.technology/我的页面',
+      '普遍接受-测试.top/我的页面',
+      'ua-test.世界/我的页面',
+      '普遍接受-测试.世界/我的页面',
+      'ختبار-القبولالعالمي.top/我的页面',
+      'اختبار-القبولالعالمي.شبكة/我的页面',
+      "www.example.com/wpstyle/?p=364",
+      "www.example.com/foo/?bar=baz&inga=42&quux",
+      "☺.damowmow.com/",
+      "مثال.إختبار",
+      "例子.测试",
+      // cSpell: enable
     ];
 
     return $this->dataEnhanceWithScheme($urls);
@@ -214,16 +202,16 @@
       // '.www.foo.bar./',
     ];
     $schemes = [
+      ['', ''],
+      ['foo.bar/', 'ftps'],
+      ['foo.com', ''],
+      ['not-a-valid-scheme', 'invalid'],
+      ['test', ''],
+      ['test', 'h'],
       // cSpell: disable
       [' shouldfail', '://'],
       ['1234', 'rdar'],
       // cSpell: enable
-      ['not-a-valid-scheme', 'invalid'],
-      ['test', 'h'],
-      ['foo.bar/', 'ftps'],
-      ['foo.com', ''],
-      ['test', ''],
-      ['', ''],
     ];
     return array_merge($schemes, $this->dataEnhanceWithScheme($data));
   }