BackstopJS: Cannot find module 'portfinder'

I’m running Backstop locally via Docker. Everything was fine and dandy, until I ran docker pull backstopjs/backstopjs today. After downloading the latest image, running the same backstop command which was previously working now throws: Error: Cannot find module portfinder.

The Backstop version in the Docker image is apparently v3.5.4, yes, even though the latest on Docker hub right now is v3.5.3.