Convert read-only sparseimage to read-write

Question

I have a big sparseimage on an external harddrive (HFS+) which I use as a backup place for some special files. After re-installing my laptop, the image is mounted as read-only. How can I convert this back to a read-write?

/dev/disk5 on /Volumes/foo (hfs, local, nodev, nosuid, read-only, noowners, mounted by me)

I'd like to avoid copying the files over to a new sparseimage, as moving hundreds of gigabytes over usb2 is not much fun.

Answer 1

I'll post this as an answer instead of deleting this question.

The culprit was a read-only foo.sparseimage file on the external harddrive. Changing the owner back to me (with read and write permission for me), everything is back to normal.