{http://www.w3.org/2001/XMLSchema}include does not support HTTPS?

[brent saner]

My apologies if there is a bug for this already but I didn't find one.

When performing a {http://www.w3.org/2001/XMLSchema}include for an XSD, I get the following:

(...)
  File "src/lxml/xmlschema.pxi", line 86, in lxml.etree.XMLSchema.__init__
lxml.etree.XMLSchemaParseError: Element '{http://www.w3.org/2001/XMLSchema}include': Failed to load the document 'https://schema.xml.r00t2.io/lib/types/aif.xsd' for inclusion., line 9

triggered via

I am using base_url and a relative include, if it makes any difference (though it does render properly to the correct URL for the included XSD as shown). It works just fine if I change the base_url to http://.

Is HTTPS not supported? I'd very much prefer to use it to ensure at least some level of fetching integrity.

VERSION INFO:
Python : sys.version_info(major=3, minor=8, micro=0, releaselevel='final', serial=0)
lxml.etree : (4, 4, 2, 0)
libxml used : (2, 9, 10)
libxml compiled : (2, 9, 10)
libxslt used : (1, 1, 34)
libxslt compiled : (1, 1, 34)