It is shown that the expansion assumed by Stewartson to describe the flow close to separation in a compressible boundary layer is incomplete. When the wall is cold an infinity of new terms involving log ξ, log log ξ and their products and quotients must be added at each algebraic stage. The skin friction then vanishes like x½ ln x where x is the distance to separation. None of the coefficients of the logarithmic terms are arbitrary and in particular the first two terms in the expansion of the skin friction are known if the heat transfer is given at separation. Convergence is so slow, however, that this is of no practical value.