diff -u b/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidatorTest.php b/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidatorTest.php
--- b/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidatorTest.php
+++ b/core/modules/link/tests/src/Unit/Plugin/Validation/Constraint/LinkExternalProtocolsConstraintValidatorTest.php
@@ -59,6 +59,8 @@
 
     // Malformed protocols.
     $data[] = ['irc:', FALSE];
+    $data[] = ['http:/www.drupal.org', FALSE];
+    $data[] = ['htp://www.drupal.org', FALSE];
 
     foreach ($data as &$single_data) {
       $url = Url::fromUri($single_data[0]);