Summary: By comparison with both experimental and numerical data, K. B. Dysthe’s \(O(\epsilon^4)\) modified nonlinear Schrödinger equation [Proc. R. Soc. Lond., Ser. A 369, 105–114 (1979; Zbl 0429.76014)] has been shown to model the evolution of a slowly varying wavetrain well (here \(\epsilon\) is the wave steepness). In this work, we extend the equation to include a prescribed, large-scale, \(O(\epsilon^2)\) surface current which varies about a mean value. As an introduction, a heuristic derivation of the \(O(\epsilon^3)\) current-modified equation, used by V. V. Bakhanov et al. [in Proc. 1996 Int. Geoscience and Remote Sensing Symposium, Vol. I (Lincoln, NE, 1996), IEEE, New York, 350–352 (1996); per. bibl.], is given, before a more formal approach is used to derive the \(O(\epsilon^4)\) equation. Numerical solutions of the new equations are compared in one horizontal dimension with those from a fully nonlinear solver for velocity potential in the specific case of a sinusoidal surface current, such as may be due to an underlying internal wave. The comparisons are encouraging, especially for the \(O(\epsilon^4)\) equation.