diff --git a/src/Form/DataTransformer/BooleanToStringTransformer.php b/src/Form/DataTransformer/BooleanToStringTransformer.php
index bc5a92ce5f..ef8fced8ad 100644
--- a/src/Form/DataTransformer/BooleanToStringTransformer.php
+++ b/src/Form/DataTransformer/BooleanToStringTransformer.php
@@ -21,7 +21,7 @@
  *
  * @author Peter Gribanov <info@peter-gribanov.ru>
  */
-class BooleanToStringTransformer implements DataTransformerInterface
+final class BooleanToStringTransformer implements DataTransformerInterface
 {
     private $trueValue;
 
diff --git a/tests/Form/DataTransformer/BooleanToStringTransformerTest.php b/tests/Form/DataTransformer/BooleanToStringTransformerTest.php
index 9e7176cf18..f5f06ff87b 100644
--- a/tests/Form/DataTransformer/BooleanToStringTransformerTest.php
+++ b/tests/Form/DataTransformer/BooleanToStringTransformerTest.php
@@ -19,7 +19,7 @@
 /**
  * @author Peter Gribanov <info@peter-gribanov.ru>
  */
-class BooleanToStringTransformerTest extends TestCase
+final class BooleanToStringTransformerTest extends TestCase
 {
     public function provideTransform(): array
     {