We report a large magnetic entropy change associated with a high-temperature martensitic transformation in Ni40Co10Mn41Sn9 (at. %) melt-spun ribbons. The ribbons underwent a first-order forward martensitic transition and a reverse structural transition from the paramagnetic six-layered modulated martensite to a ferromagnetic austenite in the temperature range of 395–380 K. For a magnetic field change of 5 T (2 T), extremely large magnetic entropy changes of 33.9 (25) J kg−1 K−1 and 53 (22) J kg−1 K−1 upon reverse and forward martensitic transformations occurred. These values are among the largest for Ni-Mn based Heusler alloys reported so far. As compared with the large values upon heating, hysteresis losses upon cooling were negligibly low (only 0.36 J kg−1). The present findings open up the possibility of elevated temperature magnetic cooling.