diff --git a/core/tests/Drupal/Tests/Core/UnroutedUrlTest.php b/core/tests/Drupal/Tests/Core/UnroutedUrlTest.php
index 66605e9..94ff9b4 100644
--- a/core/tests/Drupal/Tests/Core/UnroutedUrlTest.php
+++ b/core/tests/Drupal/Tests/Core/UnroutedUrlTest.php
@@ -80,6 +80,7 @@ public function testFromUri($uri, $is_external) {
   public function providerFromUri() {
     return [
       // [$uri, $is_external]
+      ['//drupal.org', TRUE],
       // An external URI.
       ['https://www.drupal.org', TRUE],
       // An internal, unrouted, base-relative URI.