diff --git a/django/db/models/fields/__init__.py b/django/db/models/fields/__init__.py
index 516f4b1538..f19374f08c 100644
--- a/django/db/models/fields/__init__.py
+++ b/django/db/models/fields/__init__.py
@@ -289,7 +289,7 @@ class Field(object):
         if self.choices:
             return first_choice + list(self.choices)
         rel_model = self.rel.to
-        return first_choice + [(x._get_pk_val(), str(x))
+        return first_choice + [(getattr(x, self.rel.get_related_field().attname), str(x))
                                for x in rel_model._default_manager.complex_filter(self.rel.limit_choices_to)]
 
     def get_choices_default(self):