diff --git a/src/Validators/InstanceValidator.php b/src/Validators/InstanceValidator.php
index 5978afed..f14a5de8 100644
--- a/src/Validators/InstanceValidator.php
+++ b/src/Validators/InstanceValidator.php
@@ -4,7 +4,11 @@
 
 class InstanceValidator extends BaseValidator
 {
-    private $classname;
+    /**
+    * @var string
+    */
+    protected $classname;
+    
     public function __construct($classname)
     {
         $this->classname = $classname;