How to reference methods from within the same class in f#?

I have been programming in f# for a few weeks now and decided that I would now try out some of the object oriented features. I am wondering though, how to reference a method in a class from within another method in that class. Here is an (admittedly contrived) but deliberately simple example of what I am talking about.

type MathsOperations =
    static member addOne (a : int) : int =
        a + 1

    static member addTwo (a : int) : int =
        1 + (addOne a)

Here in the addTwo method I get the error that addOne is not defined.