unique_with does not work with BooleanFields

[Jeffrey de Lange]

I have a model which has a BooleanField that determines on which path a model should be visible:

class ExampleModel(models.Model):
    title = models.CharField(max_length=255)
    is_in_A = models.BooleanField()
    slug = AutoSlugField(unique_with='is_in_A', populate_from='title', always_update=True)

The unique_with in this field does not work when the is_in_A is False.