Testing abstract model with ForeignKey to another app in django test framework

I want to test an abstract model that has a ForeignKey to a model defined in another app:

from otherapp.models import Person

class ModelMaster(models.Model):
    slave = models.ForeignKey(Person)

    class Meta:
        abstract = True

The problems arises when I just define a model inheriting from ModelMaster in tests.py:

from .models import ModelMaster

class Master(ModelMaster):
    pass

The python manage.py test breaks with the following error:

django.db.utils.ProgrammingError: relation "otherapp_person" does not exist

But when I define the Person model in the same app as the ModelMaster, there is no error.

Is there a way to make it working, so that model from another app referenced in an abstract model is properly recognised during the test?