Running tests fails in the test runner call_command

I've got a 3.2.10 installation and haven't run my unit tests in a long time. When I try now, I get a failure which seems to trace back to the test runner itself:

TypeError: Unknown option(s) for check command: databases. Valid options are: all, debug, force_color, help, names, no_color, pythonpath, quiet, settings, skip_checks, stderr, stdout, traceback, verbose, verbosity, version.

where the only mention of call_command with an explicit "databases" argument is in django/test/runner.py

I see this argument was introduced in 3.1 and was not present in 3.0.x and earlier.

Any hints on where to look for the root cause or how to patch it up?

TIA

- Tom