The Q value of the ;{112}Sn double-beta decay was determined by using a Penning trap mass spectrometer. The new atomic-mass difference between ;{112}Sn and ;{112}Cd of 1919.82(16) keV is 25 times more precise than the previous value of 1919(4) keV. This result removes the possibility of enhanced resonance capture of the neutrinoless double-EC decay to the excited 0;{+} state at 1871.00(19) keV in ;{112}Cd.