Better understanding how convective processes impact the isotopic composition of atmospheric water has implications for understanding present-day phenomena such as squall lines or tropical cyclones, and for reconstructions of past rainfall extreme events. With this motivation, we implemented water stable isotopes in the non-hydrostatic mesoscale atmospheric model Meso-NH. Water stable isotopes are implemented in the advection of water phases and in the microphysical scheme. The implementation is validated on a test case of a 2D simulation of a tropical squall line observed in June 1981 during the COPT81 field campaign in the Sahel region. The isotopic version of Meso-NH (Meso-NH-ISO) captures the expected evolution of the isotopic composition of both precipitation and water vapor along the squall line. This work opens the door to future isotopic studies using realistic cases of mesoscale convective systems (squall lines, tropical cyclones).