A turbofan comprising a motor and a nacelle, surrounding the motor, where a duct for a bypass flow is delimited between the nacelle and the motor and in which a flow of air flows. The nacelle comprises reverser flaps where each one is articulated between a stowed position in which it is not in the bypass duct and a deployed position in which it is across the bypass duct. The turbofan has at least one reverser flap with at least one leakage window configured to allow airflow in the deployed position. The at least one reverser flap has at least one fin extending across the leakage window.