How do you fold a fitted sheet?

I can never seem to fold a fitted sheet the right way since all 4 corners are not 90 degree angles. Any tips?How do you fold a fitted sheet?
The way I do it is I fold it in half then take the corners of the corresponding sides and push them into the concave of the other (kind of liking placing one bowl in another). Then I fold it in half and do the same again, this time with all four corners. At that point it's practically a square and simple to fold.