  In this paper we describe the performance of a light detector for Ar
scintillation light made of wavelength-shifting (WLS) fibers connected to
Silicon-Photomultipliers (SiPM). The setup was conceived to be used as
anti-Compton veto for high purity germanium (HPGe) detectors operated directly
in liquid Argon (LAr). Background suppression efficiencies for different
radioactive sources were measured in a test cryostat with about 800 kg LAr.
This work was part of the R\&D effort for the GERDA experiment.
