diff --git a/tests/src/Unit/TitleCaseTest.php b/tests/src/Unit/TitleCaseTest.php
index 645f13338d350e83c778832a28cc3112f8a2ffbc..6a98b92902f63f0fd28631e75205482dfff0dc89 100644
--- a/tests/src/Unit/TitleCaseTest.php
+++ b/tests/src/Unit/TitleCaseTest.php
@@ -31,6 +31,7 @@ class TitleCaseTest extends TokenModifierTestCase {
     $data['basic'] = ['hello world!', 'Hello World!'];
     $data['already capitalised'] = ['It\'s Working?', 'It\'s Working?'];
     $data['everything else capitalised'] = ['cAPITALISE eVERYTHING', 'CAPITALISE EVERYTHING'];
+    $data['multibyte'] = ['čhecking multibyte ūnderway...', 'Čhecking Multibyte Ūnderway...'];
     return $data;
   }
 
diff --git a/tests/src/Unit/UpperCaseFirstTest.php b/tests/src/Unit/UpperCaseFirstTest.php
index 950301d23f646fa11abe0727ce56262ff23cce51..82a165e90fe90e6b46102e3fbe4c6a269cc930b6 100644
--- a/tests/src/Unit/UpperCaseFirstTest.php
+++ b/tests/src/Unit/UpperCaseFirstTest.php
@@ -31,6 +31,7 @@ class UpperCaseFirstTest extends TokenModifierTestCase {
     $data['basic'] = ['hello world!', 'Hello world!'];
     $data['already capitalised'] = ['Working?', 'Working?'];
     $data['everything else capitalised'] = ['cAPITALISE', 'CAPITALISE'];
+    $data['multibyte'] = ['čhecking multibyte ūnderway...', 'Čhecking multibyte ūnderway...'];
     return $data;
   }