diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index f582a6813..dd90c3f86 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -351,7 +351,12 @@ class RelatedField(WritableField):
         if self.read_only:
             return
 
-        value = data.get(field_name)
+        try:
+            value = data[field_name]
+        except KeyError:
+            if self.required:
+                raise ValidationError(self.error_messages['required'])
+            return
 
         if value in (None, '') and not self.null:
             raise ValidationError('Value may not be null')
diff --git a/rest_framework/tests/serializer.py b/rest_framework/tests/serializer.py
index 6ea4b4246..f780e811e 100644
--- a/rest_framework/tests/serializer.py
+++ b/rest_framework/tests/serializer.py
@@ -308,6 +308,38 @@ class ModelValidationTests(TestCase):
         self.assertFalse(second_serializer.is_valid())
         self.assertEqual(second_serializer.errors,  {'title': [u'Album with this Title already exists.']})
 
+    def test_foreign_key_with_partial(self):
+        """
+        Test ModelSerializer validation with partial=True
+
+        Specifically test foreign key validation.
+        """
+
+        album = Album(title='test')
+        album.save()
+
+        class PhotoSerializer(serializers.ModelSerializer):
+            class Meta:
+                model = Photo
+
+        photo_serializer = PhotoSerializer(data={'description': 'test', 'album': album.pk})
+        self.assertTrue(photo_serializer.is_valid())
+        photo = photo_serializer.save()
+
+        # Updating only the album (foreign key)
+        photo_serializer = PhotoSerializer(instance=photo, data={'album': album.pk}, partial=True)
+        self.assertTrue(photo_serializer.is_valid())
+        self.assertTrue(photo_serializer.save())
+
+        # Updating only the description
+        photo_serializer = PhotoSerializer(instance=photo,
+                                           data={'description': 'new'},
+                                           partial=True)
+
+        self.assertTrue(photo_serializer.is_valid())
+        self.assertTrue(photo_serializer.save())
+
+
 
 class RegexValidationTest(TestCase):
     def test_create_failed(self):