diff --git a/django/forms/models.py b/django/forms/models.py
index d42b98483b..705ef10f17 100644
--- a/django/forms/models.py
+++ b/django/forms/models.py
@@ -698,7 +698,11 @@ class BaseInlineFormSet(BaseModelFormSet):
         self.save_as_new = save_as_new
         # is there a better way to get the object descriptor?
         self.rel_name = RelatedObject(self.fk.rel.to, self.model, self.fk).get_accessor_name()
-        qs = self.model._default_manager.filter(**{self.fk.name: self.instance})
+        if self.fk.rel.field_name == self.fk.rel.to._meta.pk.name:
+            backlink_value = self.instance
+        else:
+            backlink_value = getattr(self.instance, self.fk.rel.field_name)
+        qs = self.model._default_manager.filter(**{self.fk.name: backlink_value})
         super(BaseInlineFormSet, self).__init__(data, files, prefix=prefix,
                                                 queryset=qs)
 
@@ -733,7 +737,7 @@ class BaseInlineFormSet(BaseModelFormSet):
         # Use commit=False so we can assign the parent key afterwards, then
         # save the object.
         obj = form.save(commit=False)
-        setattr(obj, self.fk.get_attname(), self.instance.pk)
+        setattr(obj, self.fk.get_attname(), getattr(self.instance, self.fk.rel.field_name))
         if commit:
             obj.save()
         # form.save_m2m() can be called via the formset later on if commit=False
@@ -749,6 +753,7 @@ class BaseInlineFormSet(BaseModelFormSet):
             # The foreign key field might not be on the form, so we poke at the
             # Model field to get the label, since we need that for error messages.
             form.fields[self.fk.name] = InlineForeignKeyField(self.instance,
+                to_field=self.fk.rel.field_name,
                 label=getattr(form.fields.get(self.fk.name), 'label', capfirst(self.fk.verbose_name))
             )
 
@@ -845,8 +850,12 @@ class InlineForeignKeyField(Field):
     def __init__(self, parent_instance, *args, **kwargs):
         self.parent_instance = parent_instance
         self.pk_field = kwargs.pop("pk_field", False)
+        self.to_field = kwargs.pop("to_field", None)
         if self.parent_instance is not None:
-            kwargs["initial"] = self.parent_instance.pk
+            if self.to_field:
+                kwargs["initial"] = getattr(self.parent_instance, self.to_field)
+            else:
+                kwargs["initial"] = self.parent_instance.pk
         kwargs["required"] = False
         kwargs["widget"] = InlineForeignKeyHiddenInput
         super(InlineForeignKeyField, self).__init__(*args, **kwargs)
@@ -858,7 +867,11 @@ class InlineForeignKeyField(Field):
             # if there is no value act as we did before.
             return self.parent_instance
         # ensure the we compare the values as equal types.
-        if force_unicode(value) != force_unicode(self.parent_instance.pk):
+        if self.to_field:
+            orig = getattr(self.parent_instance, self.to_field)
+        else:
+            orig = self.parent_instance.pk
+        if force_unicode(value) != force_unicode(orig):
             raise ValidationError(self.error_messages['invalid_choice'])
         return self.parent_instance
 
diff --git a/tests/regressiontests/model_formsets_regress/__init__.py b/tests/regressiontests/model_formsets_regress/__init__.py
new file mode 100644
index 0000000000..e69de29bb2
diff --git a/tests/regressiontests/model_formsets_regress/models.py b/tests/regressiontests/model_formsets_regress/models.py
new file mode 100644
index 0000000000..51fc6a49ab
--- /dev/null
+++ b/tests/regressiontests/model_formsets_regress/models.py
@@ -0,0 +1,9 @@
+from django.db import models
+
+class User(models.Model):
+    username = models.CharField(max_length=12, unique=True)
+    serial = models.IntegerField()
+
+class UserSite(models.Model):
+    user = models.ForeignKey(User, to_field="username")
+    data = models.IntegerField()
diff --git a/tests/regressiontests/model_formsets_regress/tests.py b/tests/regressiontests/model_formsets_regress/tests.py
new file mode 100644
index 0000000000..c20c1f4077
--- /dev/null
+++ b/tests/regressiontests/model_formsets_regress/tests.py
@@ -0,0 +1,24 @@
+from django.forms.models import inlineformset_factory
+from django.test import TestCase
+
+from models import User, UserSite
+
+class InlineFormsetTests(TestCase):
+    def test_formset_over_to_field(self):
+        "A formset over a ForeignKey with a to_field can be saved. Regression for #10243"
+        FormSet = inlineformset_factory(User, UserSite)
+        user = User.objects.create(serial=1, username='apollo13')
+        user.save()
+        data = {
+            'usersite_set-TOTAL_FORMS': u'1',
+            'usersite_set-INITIAL_FORMS': u'0',
+            'usersite_set-0-data': u'10',
+            'usersite_set-0-user': u'apollo13'
+        }
+        form_set = FormSet(data, instance=user)
+        if form_set.is_valid():
+            form_set.save()
+            usersite = UserSite.objects.all().values()[0]
+            self.assertEqual(usersite, {'data': 10, 'user_id': u'apollo13', 'id': 1})
+        else:
+            self.fail('Errors found on form:%s' % form_set.errors)
\ No newline at end of file