diff --git a/src/Controller/AutocompleteController.php b/src/Controller/AutocompleteController.php
index 1e6e5bd1774845535a3cc27da21697dc19b2bdab..cbb4d2ea88963c3480a95832bb3edf961eadcf31 100644
--- a/src/Controller/AutocompleteController.php
+++ b/src/Controller/AutocompleteController.php
@@ -2,7 +2,6 @@
 
 namespace Drupal\linkit\Controller;
 
-use Drupal\Component\Utility\Unicode;
 use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
 use Drupal\Core\Entity\EntityStorageInterface;
 use Drupal\linkit\SuggestionManager;
@@ -77,7 +76,7 @@ class AutocompleteController implements ContainerInjectionInterface {
     $this->linkitProfile = $this->linkitProfileStorage->load($linkit_profile_id);
     $string = $request->query->get('q');
 
-    $suggestionCollection = $this->suggestionManager->getSuggestions($this->linkitProfile, Unicode::strtolower($string));
+    $suggestionCollection = $this->suggestionManager->getSuggestions($this->linkitProfile, mb_strtolower($string));
 
     /*
      * If there are no suggestions from the matcher plugins, we have to add a
diff --git a/src/Tests/ProfileCreationTrait.php b/src/Tests/ProfileCreationTrait.php
index e662aaf1412f8dd11aa08d19368e84fdd618aa9f..2343035689e58c5a712464ed0b39fe6deffbf40a 100644
--- a/src/Tests/ProfileCreationTrait.php
+++ b/src/Tests/ProfileCreationTrait.php
@@ -2,7 +2,6 @@
 
 namespace Drupal\linkit\Tests;
 
-use Drupal\Component\Utility\Unicode;
 use Drupal\linkit\Entity\Profile;
 
 /**
@@ -29,7 +28,7 @@ trait ProfileCreationTrait {
   protected function createProfile(array $settings = []) {
     // Populate defaults array.
     $settings += [
-      'id' => Unicode::strtolower($this->randomMachineName()),
+      'id' => mb_strtolower($this->randomMachineName()),
       'label' => $this->randomMachineName(),
     ];
 
diff --git a/tests/src/Functional/ProfileAdminTest.php b/tests/src/Functional/ProfileAdminTest.php
index 3b840b9ab4447b9911aa950e3036eedb5915838f..86b40676ccdca79e82719d7e3dd4dcb549a14827 100644
--- a/tests/src/Functional/ProfileAdminTest.php
+++ b/tests/src/Functional/ProfileAdminTest.php
@@ -2,7 +2,6 @@
 
 namespace Drupal\Tests\linkit\Functional;
 
-use Drupal\Component\Utility\Unicode;
 use Drupal\linkit\Tests\ProfileCreationTrait;
 
 /**
@@ -62,8 +61,8 @@ class ProfileAdminTest extends LinkitBrowserTestBase {
 
     // Create a profile.
     $edit = [];
-    $edit['label'] = Unicode::strtolower($this->randomMachineName());
-    $edit['id'] = Unicode::strtolower($this->randomMachineName());
+    $edit['label'] = mb_strtolower($this->randomMachineName());
+    $edit['id'] = mb_strtolower($this->randomMachineName());
     $edit['description'] = $this->randomMachineName(16);
     $this->submitForm($edit, t('Save and manage matchers'));
 
diff --git a/tests/src/Kernel/LinkitAutocompleteTest.php b/tests/src/Kernel/LinkitAutocompleteTest.php
index 5c167b869563c5a7a8c23e34c6ebc82bfc6b6773..912d777d2a415b25cb92d597c8c77e571f00f5ed 100644
--- a/tests/src/Kernel/LinkitAutocompleteTest.php
+++ b/tests/src/Kernel/LinkitAutocompleteTest.php
@@ -5,7 +5,6 @@ namespace Drupal\Tests\linkit\Kernel;
 use Drupal\Component\Render\FormattableMarkup;
 use Drupal\Component\Serialization\Json;
 use Drupal\Component\Utility\Html;
-use Drupal\Component\Utility\Unicode;
 use Drupal\entity_test\Entity\EntityTest;
 use Drupal\entity_test\Entity\EntityTestMul;
 use Drupal\language\Entity\ConfigurableLanguage;
@@ -221,7 +220,7 @@ class LinkitAutocompleteTest extends LinkitKernelTestBase {
   protected function createProfile(array $settings = []) {
     // Populate defaults array.
     $settings += [
-      'id' => Unicode::strtolower($this->randomMachineName()),
+      'id' => mb_strtolower($this->randomMachineName()),
       'label' => $this->randomMachineName(),
     ];
 
diff --git a/tests/src/Kernel/LinkitKernelTestBase.php b/tests/src/Kernel/LinkitKernelTestBase.php
index 737a0bb1f4e5972ea95d688ce919318029cc24f6..4a8bde6fde3c9223b1e1055e493bc125d127cc0a 100644
--- a/tests/src/Kernel/LinkitKernelTestBase.php
+++ b/tests/src/Kernel/LinkitKernelTestBase.php
@@ -51,7 +51,7 @@ abstract class LinkitKernelTestBase extends KernelTestBase {
     if ($permissions) {
       // Create a new role and apply permissions to it.
       $role = Role::create([
-        'id' => strtolower($this->randomMachineName(8)),
+        'id' => mb_strtolower($this->randomMachineName(8)),
         'label' => $this->randomMachineName(8),
       ]);
       $role->save();
diff --git a/tests/src/Kernel/Matchers/TermMatcherTest.php b/tests/src/Kernel/Matchers/TermMatcherTest.php
index 22f2c446e68db8d1560413dc2619e8e6784a4332..4e04d0fde9bca5eef604cb2762c009546bbd4550 100644
--- a/tests/src/Kernel/Matchers/TermMatcherTest.php
+++ b/tests/src/Kernel/Matchers/TermMatcherTest.php
@@ -2,7 +2,6 @@
 
 namespace Drupal\Tests\linkit\Kernel\Matchers;
 
-use Drupal\Component\Utility\Unicode;
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\taxonomy\VocabularyInterface;
 use Drupal\Tests\linkit\Kernel\LinkitKernelTestBase;
@@ -118,7 +117,7 @@ class TermMatcherTest extends LinkitKernelTestBase {
     $vocabulary = $vocabularyStorage->create([
       'name' => $name,
       'description' => $name,
-      'vid' => Unicode::strtolower($name),
+      'vid' => mb_strtolower($name),
       'langcode' => LanguageInterface::LANGCODE_NOT_SPECIFIED,
     ]);
     $vocabulary->save();