Missing a Rakaah and Salaam with Imam

Q: I joined the jamaat after missing one rakaat. When the Imam made salaam at the end of the salaah, by mistake I also made salaam. Realising my mistake, I immediately stood up. I had turned my head completely when making the salaam. I then proceeded to fill in the missed rakaat. Was my salaah valid?

A: Your salaah was valid but you had to make sajda sahu for that error.