diff --git a/django/forms/models.py b/django/forms/models.py
index 430dd4d7cc..96e2008e3f 100644
--- a/django/forms/models.py
+++ b/django/forms/models.py
@@ -48,10 +48,6 @@ def construct_instance(form, instance, fields=None, exclude=None):
             continue
         if exclude and f.name in exclude:
             continue
-        # OneToOneField doesn't allow assignment of None. Guard against that
-        # instead of allowing it and throwing an error.
-        if isinstance(f, models.OneToOneField) and cleaned_data[f.name] is None:
-            continue
         # Defer saving file-type fields until after the other fields, so a
         # callable upload_to can use the values from other fields.
         if isinstance(f, models.FileField):
diff --git a/tests/regressiontests/model_forms_regress/models.py b/tests/regressiontests/model_forms_regress/models.py
index 23ac745274..871bb6f815 100644
--- a/tests/regressiontests/model_forms_regress/models.py
+++ b/tests/regressiontests/model_forms_regress/models.py
@@ -47,3 +47,10 @@ class RealPerson(models.Model):
         if self.name.lower() == 'anonymous':
             raise ValidationError("Please specify a real name.")
 
+class Author(models.Model):
+    publication = models.OneToOneField(Publication, null=True, blank=True)
+    full_name = models.CharField(max_length=255)
+
+class Author1(models.Model):
+    publication = models.OneToOneField(Publication, null=False)
+    full_name = models.CharField(max_length=255)
diff --git a/tests/regressiontests/model_forms_regress/tests.py b/tests/regressiontests/model_forms_regress/tests.py
index c923a12e15..d03e61d4fa 100644
--- a/tests/regressiontests/model_forms_regress/tests.py
+++ b/tests/regressiontests/model_forms_regress/tests.py
@@ -6,7 +6,7 @@ from django.forms.models import modelform_factory
 from django.conf import settings
 from django.test import TestCase
 
-from models import Person, RealPerson, Triple, FilePathModel, Article, Publication, CustomFF
+from models import Person, RealPerson, Triple, FilePathModel, Article, Publication, CustomFF, Author, Author1
 
 
 class ModelMultipleChoiceFieldTests(TestCase):
@@ -152,3 +152,35 @@ class ModelClassTests(TestCase):
         class NoModelModelForm(forms.ModelForm):
             pass
         self.assertRaises(ValueError, NoModelModelForm)
+
+class OneToOneFieldTests(TestCase):
+    def test_assignment_of_none(self):
+        class AuthorForm(forms.ModelForm):
+            class Meta:
+                model = Author
+                fields = ['publication', 'full_name']
+
+        publication = Publication.objects.create(title="Pravda",
+            date_published=date(1991, 8, 22))
+        author = Author.objects.create(publication=publication, full_name='John Doe')
+        form = AuthorForm({'publication':u'', 'full_name':'John Doe'}, instance=author)
+        self.assert_(form.is_valid())
+        self.assertEqual(form.cleaned_data['publication'], None)
+        author = form.save()
+        # author object returned from form still retains original publication object
+        # that's why we need to retreive it from database again
+        new_author = Author.objects.get(pk=author.pk)
+        self.assertEqual(new_author.publication, None)
+
+    def test_assignment_of_none_null_false(self):
+        class AuthorForm(forms.ModelForm):
+            class Meta:
+                model = Author1
+                fields = ['publication', 'full_name']
+
+        publication = Publication.objects.create(title="Pravda",
+            date_published=date(1991, 8, 22))
+        author = Author1.objects.create(publication=publication, full_name='John Doe')
+        form = AuthorForm({'publication':u'', 'full_name':'John Doe'}, instance=author)
+        self.assert_(not form.is_valid())
+