Fast sea-ice edge plays a dominant role in positioning of flaw polynyas – winter sea-ice production and dense water formation areas of the Arctic shelf seas. In this study we integrate the Laptev Sea fast ice into a coupled sea-ice–ocean model. Prior to parameterization the simulated flaw polynya did not occur at the fast-ice edge, but directly at the coast instead. The dislocation of the polynya resulted in severe regional biases in sea-ice and ocean parameters. After including the landfast ice in the model the polynya is positioned correctly, thus significantly improving the representation of sea-ice concentration, ocean temperature and salinity distribution. The results of the improved model reflect the importance of the fast ice for the shelf circulation. The model run with the fast ice results in stronger stratification, enhanced estuarine circulation and dense water formation compared with the model run without the fast ice. The validation of the ice concentration with the satellite remote-sensing products shows satisfactory results. The ocean parameters still need to be validated with the observational data.