Intern - window is undefined

I have a loop of tests running in intern-geezer, with about twenty out of a hundred very similar tests running successfully. Then suddenly:

FATAL ERROR
ReferenceError: window is not defined

and the loop stops. There are no explicit calls to window or document in my code. It's pure JS. I'm using intern-geezer, 2.2.2. The line numbers referenced in the error stack make absolutely no sense. They're way off.

I've read the suggestion to switch from the command:

./node_modules/.bin/intern-client config=tests/intern

to:

./node_modules/.bin/intern-runner config=tests/intern

but I don't want to connect to a server or open a browser (there's a separate, strange loading error occurring there which seems specific to geezer). I want to get this going at the command line. Grateful for any help, I'm totally new to Intern.