We report the discovery of maser emission in the two lowest rotational transitions of CS toward the high-mass protostar W51 e2e with ALMA and the JVLA. The masers from CS J=1-0 and J=2-1 are neither spatially nor spectrally coincident (they are separated by ~150 AU and ~30 km/s), but both appear to come from the base of the blueshifted outflow from this source. These CS masers join a growing list of rarely-detected maser transitions that may trace a unique phase in the formation of high-mass protostars.
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