In this article, we consider the linear stability of the two-dimensional flow induced by the linear stretching of a surface in the streamwise direction. The basic flow is a rare example of an exact analytical solution of the Navier–Stokes equations. Using results from a large Reynolds number asymptotic study and a highly accurate spectral numerical method, we show that this flow is linearly unstable to disturbances in the form of Tollmien–Schlichting waves. Previous studies have shown that this flow is linearly stable. However, our results show that this is only true for Görtler-type disturbances.