A class of adaptive control schemes, motivated from nonlinear systems theory, has been proposed for minimum phase linear time invariant plants. Under certain assumptions on the plant transfer function, these schemes guarantee uniform signal boundedness and good transient and steady state response for the regulation or tracking error. In this paper we propose a modification that improves the robustness of these schemes with respect to a class of multiplicative uncertainties, without loss of performance. The parameter convergence properties of the proposed schemes are examined when the reference signal is dominantly rich.