In the recently introduced flamelet-generated manifold (FGM) method the ideas of the manifold and the flamelet approach are combined: a manifold is constructed using one-dimensional flamelets. In this paper the effect of flame stretch on theaccuracy of the FGM method is investigated. In order to isolate the effect of flame stretch, premixed methane/air counterflow flames are simulated. In the case of unit Lewis numbers a one-dimensional manifold is sufficient to model the main effects of flame stretch. A manifold with two progress variables reproduces the results computed using detailed kinetics almost exactly. When non-unit Lewis numbersare used, the enthalpy and element composition of the burnt mixture change, which may influence the mass burning rate significantly. If these composition changes are included in the manifold using one additional controlling variable, the results agreewell with detailed computations.