gistfile1

diff --git a/django/db/models/fields/related.py b/django/db/models/fields/related.py
index ae792a3..c18907c 100644
--- a/django/db/models/fields/related.py
+++ b/django/db/models/fields/related.py
@@ -595,7 +595,10 @@ def create_many_related_manager(superclass, rel):
             Returns the correct value for this relationship's foreign key. This
             might be something else than pk value when to_field is used.
             """
-            fk = self.through._meta.get_field(field_name)
+            try:
+                fk = self.through._meta.get_field(field_name)
+            except AttributeError:
+                return obj.pk
             if fk.rel.field_name and fk.rel.field_name != fk.rel.to._meta.pk.attname:
                 attname = fk.rel.get_related_field().get_attname()
                 return fk.get_prep_lookup('exact', getattr(obj, attname))