TypeError: '<' not supported between instances of 'Facet3D' and 'Facet3D'

[salfter]

I'm getting this error when I try to normalize a file:

Traceback (most recent call last):
  File "/usr/bin/stl_normalize", line 1276, in <module>
    main()
  File "/usr/bin/stl_normalize", line 1265, in main
    stl.write_file(args.outfile, binary=args.write_binary)
  File "/usr/bin/stl_normalize", line 784, in write_file
    self._write_ascii_file(filename)
  File "/usr/bin/stl_normalize", line 748, in _write_ascii_file
    for facet in self.facets.sorted():
  File "/usr/bin/stl_normalize", line 605, in sorted
    for pt in sorted(vals):
TypeError: '<' not supported between instances of 'Facet3D' and 'Facet3D'

I'm using Python 3.8 on Gentoo Linux, if it matters.