diff --git a/lib/xos-genx/xosgenx/targets/mock_classes.xtarget b/lib/xos-genx/xosgenx/targets/mock_classes.xtarget
index bbc5ae2..00db7e5 100644
--- a/lib/xos-genx/xosgenx/targets/mock_classes.xtarget
+++ b/lib/xos-genx/xosgenx/targets/mock_classes.xtarget
@@ -95,7 +95,7 @@
     def leaf_model(self):
         return self
 
-    def save(self):
+    def save(self, update_fields=[]):
         if self.objects:
             self.objects.save(self)