Checklist

• I have verified that that issue exists against themaster branch of Django REST framework.
• I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
• This is not a usage question. (Those should be directed to thediscussion group instead.)
• This cannot be dealt with as a third party library. (We prefer new functionality to bein the form of third party libraries where possible.)
• I have reduced the issue to the simplest possible case.
• I have included a failing test as a pull request. (If you are unable to do so we can still accept the issue.)

Steps to reproduce

importdjangodjango.setup()fromdjango.contrib.authimportget_user_modelfromdjango.dbimportmodelsfromdjango.confimportsettingsfromrest_frameworkimportserializers,testclassItem(models.Model):user=models.ForeignKey(settings.AUTH_USER_MODEL,on_delete=models.CASCADE)item_number=models.IntegerField()classMeta:unique_together= (('user','item_number'),)classItemSerializer(serializers.ModelSerializer):user=serializers.PrimaryKeyRelatedField(read_only=True,default=serializers.CurrentUserDefault())classMeta:model=Itemfields= ('id','item_number','user')User=get_user_model()user=User.objects.create_user(username='asdf')request=test.APIRequestFactory().post('/')request.user=useritem=Item.objects.create(user=user,item_number=3)data= {'item_number':item.item_number}context= {'request':request}serializer=ItemSerializer(data=data,context=context)assertnotserializer.is_valid(),'Should be False!'

Expected behavior

The serializer should not be valid. This is the case using djangorestframework == 3.3.0

Actual behavior

The serializer is valid. This is the case using djangorestframework == 3.4.0

I've tracked the root of the issue and it seems to be pull request#4192, where a new condition is added toget_unique_together_validators(): "and not field.read_only"