In our original publication concerning the Q-value determination for the ²¹Na→²¹Ne and ²³Mg→²³Na mirror-nuclei decays, the ionization energy was not included. The Q values of the presented β decays, hence, change by 17 eV in the case of ²¹Na→²¹Ne and 3 eV in the case of ²³Mg→²³Na. The essence of the paper, namely, the calculated Ft values and the resulting V_ud element of the CKM-quark-mixing matrix are not affected due to dominating uncertainties in the other relevant quantities. Equation (4) in the original publication now reads (Farmula Presented).