diff --git a/django/forms/models.py b/django/forms/models.py
index 9e6cab8..84da2f7 100644
--- a/django/forms/models.py
+++ b/django/forms/models.py
@@ -876,7 +876,11 @@ class BaseInlineFormSet(BaseModelFormSet):
             form.data[form.add_prefix(self.fk.name)] = None

         # Set the fk value here so that the form can do its validation.
-        setattr(form.instance, self.fk.get_attname(), self.instance.pk)
+        fk_value = self.instance.pk
+        if self.fk.rel.field_name != self.fk.rel.to._meta.pk.name:
+            fk_value = getattr(self.instance, self.fk.rel.field_name)
+            fk_value = getattr(fk_value, 'pk', fk_value)
+        setattr(form.instance, self.fk.get_attname(), fk_value)
         return form

     @classmethod
diff --git a/tests/model_formsets_regress/tests.py b/tests/model_formsets_regress/tests.py
index 7d400d2..a010b9f 100644
--- a/tests/model_formsets_regress/tests.py
+++ b/tests/model_formsets_regress/tests.py
@@ -154,6 +154,18 @@ class InlineFormsetTests(TestCase):
         else:
             self.fail('Errors found on formset:%s' % form_set.errors)

+    def test_inline_model_with_to_field(self):
+        "An inline model with a to_field of a formset with instance have working relations. Regression for #13794"
+        FormSet = inlineformset_factory(User, UserSite, exclude=('is_superuser',))
+
+        user = User.objects.create(username="guido", serial=1337)
+        UserSite.objects.create(user=user, data=10)
+        formset = FormSet(instance=user)
+
+        formset[0]
+        # Testing the inline model's relation
+        self.assertEqual(formset[0].instance.user_id, "guido")
+
     def test_formset_with_none_instance(self):
         "A formset with instance=None can be created. Regression for #11872"
         Form = modelform_factory(User, fields="__all__")
--
1.7.9.5