diff --git a/lib/classes/OAuth2/Bridge/ClientRepository.php b/lib/classes/OAuth2/Bridge/ClientRepository.php
index b6fd4f6a85624ca00f36ccd6584a78f0885e0f59..526e8397ade19c65498f4c4aa5cea25e49274444 100644
--- a/lib/classes/OAuth2/Bridge/ClientRepository.php
+++ b/lib/classes/OAuth2/Bridge/ClientRepository.php
@@ -37,9 +37,10 @@ class ClientRepository implements ClientRepositoryInterface
      */
     public function validateClient($clientIdentifier, $clientSecret, $grantType): bool
     {
-        if ($grantType !== 'authorization_code') {
+        if (!in_array($grantType, ['authorization_code', 'refresh_token'])) {
             return false;
         }
+
         $client = Client::findActive($clientIdentifier);
         if (!$client) {
             return false;