Refspec matches more than one

I was trying to push to a canonical repository this morning and got the following error:

$ git push origin master
error: src refspec master matches more than one.
error: failed to push some refs to 'ssh://user@host/srv/git/repo'

This happened because I had accidentally created a master tag locally:

$ git tag
master
tag1
tag2
tag3
tag4

Once I deleted the tag locally:

tag -d master

I was able to push again.