diff --git a/src/Grant/AuthCodeGrant.php b/src/Grant/AuthCodeGrant.php
index 60582d2b..8ac69270 100644
--- a/src/Grant/AuthCodeGrant.php
+++ b/src/Grant/AuthCodeGrant.php
@@ -259,7 +259,7 @@ class AuthCodeGrant extends AbstractGrant
         $accessToken->setSession($session);
         $accessToken->save();
 
-        if ($refreshToken && $this->server->hasGrantType('refresh_token')) {
+        if (isset($refreshToken) && $this->server->hasGrantType('refresh_token')) {
             $refreshToken->setAccessToken($accessToken);
             $refreshToken->save();
         }