diff --git a/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationUrl.php b/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationUrl.php
index dcafb77..0627107 100644
--- a/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationUrl.php
+++ b/core/modules/language/src/Plugin/LanguageNegotiation/LanguageNegotiationUrl.php
@@ -183,7 +183,7 @@ public function processOutbound($path, &$options = array(), Request $request = N
         }
 
         // Add Drupal's subfolder from the base_path if there is one.
-        $options['base_url'] .= rtrim($request->getBaseUrl(), '/');
+        $options['base_url'] .= $request->getBasePath();
         if ($bubbleable_metadata) {
           $bubbleable_metadata->addCacheContexts(['languages:' . LanguageInterface::TYPE_URL, 'url.site']);
         }
diff --git a/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php b/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
index 3f7994b..e1492c1 100644
--- a/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
+++ b/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
@@ -480,6 +480,8 @@ function testLanguageDomain() {
     $this->container->get('request_stack')->push($request);
     $italian_url = Url::fromRoute('system.admin', [], ['language' => $languages['it']])->toString();
     $correct_link = 'https://' . $link;
+    debug('expected link: ' . $correct_link);
+    debug('actual link: ' . $italian_url);
     $this->assertTrue($italian_url == $correct_link, format_string('The right URL (via current URL scheme) (@url) in accordance with the chosen language', array('@url' => $italian_url)));
   }