"Ambiguous information for ref" error

So I'm trying to set up a bare repository with a branch that tracks a
remote ref that isn't the one I'm mirroring.  So, I run

git clone --mirror <origin> .
git remote add -f other <remote>
git branch --track other remotes/other/master

But I'm getting the error "error: Not tracking: ambiguous information
for ref refs/remotes/other/master".  Googling this error only gave the
place in the git source code where it is returned, which seems to
indicate that it happens when there is more than one tracking match
(tracking.matches > 1).  But I'm not sure exactly what that means.
Any advice would be appreciated.  Thanks!

-- 
Tavian Barnes