diff -u b/core/modules/system/tests/src/Unit/Transliteration/MachineNameControllerTest.php b/core/modules/system/tests/src/Unit/Transliteration/MachineNameControllerTest.php
--- b/core/modules/system/tests/src/Unit/Transliteration/MachineNameControllerTest.php
+++ b/core/modules/system/tests/src/Unit/Transliteration/MachineNameControllerTest.php
@@ -50,10 +50,12 @@
       array(array('text' => 'Bob', 'langcode' => 'en', 'replace' => 'Alice', 'replace_pattern' => 'Tom'), '"Bob"'),
       array(array('text' => 'Äwesome', 'langcode' => 'en', 'lowercase' => TRUE), '"awesome"'),
       array(array('text' => 'Äwesome', 'langcode' => 'de', 'lowercase' => TRUE), '"aewesome"'),
-      array(array('text' => 'B?!"\/-ob', 'langcode' => 'en', 'lowercase' => TRUE, 'replace' => '_', 'replace_pattern' => '[^a-z0-9_.]+'), '"b_ob"'),
-      array(array('text' => 'B?!"\/-ob@e', 'langcode' => 'en', 'lowercase' => TRUE, 'replace' => '_', 'replace_pattern' => '[^a-z0-9_.]+'), '"b_ob_e"'),
-      array(array('text' => 'a@e\0', 'langcode' => 'en', 'lowercase' => TRUE, 'replace' => '_', 'replace_pattern' => '[^a-z0-9_.]+'), '"a_e_0"'),
-      array(array('text' => 'a@e\0', 'langcode' => 'en', 'lowercase' => TRUE, 'replace' => '_', 'replace_pattern' => '[^a-z0-9_.@]+'), '"a@e_0"'),
+      // Tests special characters replacement in the input text.
+      array(array('text' => 'B?!"@\/-ob@e', 'langcode' => 'en', 'lowercase' => TRUE, 'replace' => '_', 'replace_pattern' => '[^a-z0-9_.]+'), '"b_ob_e"'),
+      // Tests @ character in the replace_pattern regex.
+      array(array('text' => 'Bob@e\0', 'langcode' => 'en', 'lowercase' => TRUE, 'replace' => '_', 'replace_pattern' => '[^a-z0-9_.@]+'), '"bob@e_0"'),
+      // Tests null byte in the replace_pattern regex.
+      array(array('text' => 'Bob', 'langcode' => 'en', 'lowercase' => TRUE, 'replace' => '_', 'replace_pattern' => "@e\0"), '"bob"'),
     );
   }