The GN model of nonlinear fiber propagation has been shown to overestimate the variance of nonlinearity due to the signal Gaussianity approximation, leading to maximum reach predictions for realistic optical systems, which may be pessimistic by about 5% to 15%, depending on fiber type and system setup. Analytical corrections have been proposed, which, however, substantially increase the model complexity. In this paper, we provide a simple closed-form GN model correction formula, derived from the EGN model, which we show to be quite effective in correcting for the GN model tendency to overestimate nonlinearity. The formula also permits to clearly identify the correction dependence on key system parameters, such as span length and loss.