We report on the effects of B additions to Alloy 617 on its high-temperature oxidation behavior and on the spallation of oxide scales. Alloy 617 and a B-added derivative (Alloy 617B) were oxidized at 1050 °C in air and comparatively studied. Cr2O3 scales formed on both alloys with a spinel phase and a Ti-rich oxide on top. While both alloys showed similar scale growth kinetics, Alloy 617B showed substantially enhanced resistance to oxide scale spallation. B segregation at Cr2O3 grain boundaries, detected by atom probe tomography, was found to be the reason for the enhanced spallation resistance of Alloy 617B.