git pull error: error: ref remoto está no mas esperado

Mensagem completa:

error: Ref refs/remotes/origin/user is at 3636498c2ea7735fdcedc9af5ab3c8689e6abe77 but expected a21359c6cc2097c85775cde6a40105f4bd7100ec
From github.com:{github project url}
 ! a21359c..6273ffc  user -> origin/user  (unable to update local ref)