Filter Wagtail API response by two fields instead of just one

Question

I'm using the Wagtail API (built on top of Django Rest Framework) to request information from our site. I know that I can filter the response by an APIField using the field name and a value: https://docs.wagtail.io/en/v2.5/advanced_topics/api/v2/usage.html#filtering

However I'd like to allow for a compound filter like so: ?slug=my-url-slug&foo=bar

The result of which would only return records which matched both criteria.

UPDATE Here's some snippets of code for reference:

class LandingPageBase(Page):
    """
    LandingPageBase represents the base information needed for Eventbrite landing pages
    """
    url_slug = models.SlugField(
        max_length=255,
        allow_unicode=True,
        help_text='The slugified portion of a landing page url. Ex: sell-tickets',
    )
    locale = ParentalKey('home.Locale', on_delete=models.PROTECT, related_name='landing_pages')

    api_fields = [
        APIField('url_slug'),
        APIField('locale_code'),
        APIField('locale', serializer=serializers.StringRelatedField(source='locale_code')),
    ]

    @property
    def locale_code(self):
        return self.locale.code

And here's the URL I'm using. http://localhost:32815/api/v2/page/?locale_code=de_de&url_slug=my-cool-landing-page-french&type=landing.RawHtmlLandingPage

I interpret this query to say "Give me a record that has X locale_code, Y url_slug, and Z type", in other words all AND statements. But instead what's happening is that I get the record for the url_slug and the locale_code doesn't seem to affect the result.