The combustion properties of hydrogen make premixed hydrogen-air ?ames very prone to boundary layer ?ashback. This paper describes the improvement and extension of a bound- ary layer ?ashback model from Hoferichter  for ?ames con- ?ned in burner ducts. The original model did not perform well at higher preheat temperatures and overpredicted the backpres- sure of the ?ame at ?ashback by 4-5x. By simplifying the Lewis number dependent ?ame speed computation and by applying a generalized version of Stratford's ?ow separation criterion , the prediction accuracy is improved signi?cantly. The effect of adverse pressure gradient ?ow on the ?ashback limits in 2? and 4? diffusers is also captured adequately by coupling the model to ?ow simulations and taking into account the increased ?ow sep- aration tendency in diffuser ?ow. Future research will focus on further experimental validation and direct numerical simulations to gain better insight into the role of the quenching distance and turbulence statistics.