HARPS-N spectrum zoomed onto the NaI doublet. The main absorption lines contain an additional narrow feature blueshifted with respect to their centre. These secondary lines are not visible in other spectral lines. Therefore, we exclude contamination from the nearby stellar companion as the cause of this additional absorption. These features have a constant relative position with respect to the main absorption lines of ∼15.5 km/s. We attribute this observation to interstellar absorption.