diff --git a/core/modules/system/tests/src/Kernel/Mail/MailTest.php b/core/modules/system/tests/src/Kernel/Mail/MailTest.php
index 480d0e9..1200e85 100644
--- a/core/modules/system/tests/src/Kernel/Mail/MailTest.php
+++ b/core/modules/system/tests/src/Kernel/Mail/MailTest.php
@@ -78,7 +78,11 @@ public function testPluggableFramework() {
    */
   public function testErrorMessageDisplay() {
     // Switch mail backends.
-    $this->config('system.mail')->set('interface.default', 'test_php_mail_failure')->save();
+    // @todo can this be avoided?
+    // KernelTestBase enforces the usage of 'test_mail_collector' plugin for
+    // collect the mails. Since we need to test this functionality itself, we
+    // manually configure the default mail interface.
+    $GLOBALS['config']['system.mail']['interface']['default'] = 'test_php_mail_failure';
 
     // Test with errors displayed to users.
     \Drupal::service('plugin.manager.mail')->mail('default', 'default', 'test@example.com', 'en');
@@ -119,8 +123,6 @@ public function testCancelMessage() {
   public function testFromAndReplyToHeader() {
     $language = \Drupal::languageManager()->getCurrentLanguage();
 
-    // Use the state system collector mail backend.
-    $this->config('system.mail')->set('interface.default', 'test_mail_collector')->save();
     // Reset the state variable that holds sent messages.
     \Drupal::state()->set('system.test_mail_collector', []);
     // Send an email with a reply-to address specified.