The QEC value of the superallowed β + -emitter 42 Sc has been measured with the JYFLTRAP Penning-trap mass spectrometer at the University of Jyväskylä to be 6426.350(53) keV. This result is at least a factor of four more precise than all previous measurements, which were also inconsistent with one another. As a byproduct we determine the excitation energy of the 7 + isomeric state in 42 Sc to be 616.762(46) keV, which deviates by 8σ from the previous measurement.