diff --git a/src/OAuth2/GrantType/RefreshToken.php b/src/OAuth2/GrantType/RefreshToken.php
index 75c611f1d..d1d477c9e 100644
--- a/src/OAuth2/GrantType/RefreshToken.php
+++ b/src/OAuth2/GrantType/RefreshToken.php
@@ -15,7 +15,7 @@ class RefreshToken implements GrantTypeInterface
     /**
      * @var array
      */
-    private $refreshToken;
+    protected $refreshToken;
 
     /**
      * @var RefreshTokenInterface