Docker-compose works locally but not with docker-machine

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docker-compose.yml

db:
  image: mongo:3
  volumes:
    - ./mongo_data:/data/db

This works locally, with files being stored on the host at /data/db.

With docker-machine on macOS I get the following error:

db_1 | 2017-02-03T10:16:14.839+0000 I STORAGE [initandlisten] exception in initAndListen: 20 Attempted to create a lock file on a read-only directory: /data/db, terminating

/data/db is on the mongo image, so I’m a bit confused as to why that would be different.

ETA: Seems to be something to do with the volumes mount.