Index: newforms/models.py
===================================================================
--- newforms/models.py	(revision 7681)
+++ newforms/models.py	(working copy)
@@ -410,8 +410,11 @@
         Returns this FormSet's queryset, but restricted to children of 
         self.instance
         """
-        kwargs = {self.fk.name: self.instance}
-        return self.model._default_manager.filter(**kwargs)
+        if self.instance.pk:
+            kwargs = {self.fk.name: self.instance}
+            return self.model._default_manager.filter(**kwargs)
+        else:
+            return self.model._default_manager.get_empty_query_set()
 
     def save_new(self, form, commit=True):
         kwargs = {self.fk.get_attname(): self.instance.pk}