diff --git a/src/Type/Types/ClassStringType.php b/src/Type/Types/ClassStringType.php
index 9b4db37..b592871 100644
--- a/src/Type/Types/ClassStringType.php
+++ b/src/Type/Types/ClassStringType.php
@@ -11,6 +11,7 @@ use CuyZ\Valinor\Type\Type;
 use CuyZ\Valinor\Type\Types\Exception\CannotCastValue;
 use CuyZ\Valinor\Type\Types\Exception\InvalidClassString;
 use CuyZ\Valinor\Type\Types\Exception\InvalidUnionOfClassString;
+use CuyZ\Valinor\Utility\IsSingleton;
 use CuyZ\Valinor\Utility\Reflection\Reflection;
 
 use function is_object;
@@ -20,6 +21,8 @@ use function method_exists;
 /** @internal */
 final class ClassStringType implements StringType, CompositeType
 {
+    use IsSingleton;
+
     /** @var ObjectType|UnionType|null */
     private ?Type $subType;
 
diff --git a/tests/Unit/Type/Types/ClassStringTypeTest.php b/tests/Unit/Type/Types/ClassStringTypeTest.php
index 6b018f0..a5df6da 100644
--- a/tests/Unit/Type/Types/ClassStringTypeTest.php
+++ b/tests/Unit/Type/Types/ClassStringTypeTest.php
@@ -8,6 +8,7 @@ use CuyZ\Valinor\Tests\Fake\Type\FakeObjectCompositeType;
 use CuyZ\Valinor\Tests\Fake\Type\FakeObjectType;
 use CuyZ\Valinor\Tests\Fake\Type\FakeType;
 use CuyZ\Valinor\Tests\Fixture\Object\StringableObject;
+use CuyZ\Valinor\Tests\Traits\TestIsSingleton;
 use CuyZ\Valinor\Type\Types\Exception\InvalidUnionOfClassString;
 use CuyZ\Valinor\Type\Types\NativeStringType;
 use CuyZ\Valinor\Type\Types\ClassStringType;
@@ -24,6 +25,8 @@ use stdClass;
 
 final class ClassStringTypeTest extends TestCase
 {
+    use TestIsSingleton;
+
     public function test_string_subtype_can_be_retrieved(): void
     {
         $subType = new FakeObjectType();