diff --git a/adminsortable2/admin.py b/adminsortable2/admin.py
index 664d8ba..5647c30 100644
--- a/adminsortable2/admin.py
+++ b/adminsortable2/admin.py
@@ -485,10 +485,11 @@ def save_new(self, form, commit=True):
         """
         obj = super().save_new(form, commit=False)
 
-        order_field_value = getattr(obj, self.default_order_field, None)
-        if order_field_value is None or order_field_value >= 0:
-            max_order = self.get_max_order()
-            setattr(obj, self.default_order_field, max_order + 1)
+        if self.default_order_field:
+            order_field_value = getattr(obj, self.default_order_field, None)
+            if order_field_value is None or order_field_value >= 0:
+                max_order = self.get_max_order()
+                setattr(obj, self.default_order_field, max_order + 1)
         if commit:
             obj.save()
         # form.save_m2m() can be called via the formset later on