diff --git a/jupyter/base/values/values.yaml b/jupyter/base/values/values.yaml
index c901f15..d4f361a 100644
--- a/jupyter/base/values/values.yaml
+++ b/jupyter/base/values/values.yaml
@@ -24,7 +24,7 @@ hub:
         url = 'https://' + os.environ['NEXTCLOUD_HOST'] + '/index.php/apps/oauth2/api/v1/token'
         code = refresh_token
         data = {
-          'grant_type': refresh_token,
+          'grant_type': 'refresh_token',
           'code': code,
           'refresh_token': refresh_token,
           'client_id': client_id,