On the galaxy surrounding the BL Lacertae object MS 0205.7+3509.

We present high spatial resolution optical images of the BL Lac object MS 0205.7+3509 in the R filter, that allow us to discuss and clarify its anomalous properties. The source was previously claimed to be surrounded by a nebulosity de-centered with respect to the bright nucleus. In addition the host was claimed to be a disc dominated galaxy, contrary to the large majority of the hosts of BL Lacs. We find that there is a companion galaxy at about 2" from MS 0205.7+3509, which is responsible for many of the anomalous properties reported for this source. The observations are discussed in the context of the microlensing hypothesis for BL Lacs.