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Correction factors for reference dosimetry in magnetic resonance (MR) imaging-guided radiation therapy (kB→,M,Q) are often determined in setups that combine a conventional 6 MV linac with an electromagnet. This study investigated whether results based on these measurements were applicable for a 7 MV MR-linac using Monte Carlo simulations. For a Farmer-type ionization chamber, kB→,M,Q was assessed for different tissue-phantom ratios (TPR20,10). kB→,M,Q differed by 0.0029(43) between TPR20,10=0.6790(23)(6 MV linac) and TPR20,10=0.7028(14) (7 MV MR-linac) at 1.5T. The agreement was best in an orientation in which the secondary electrons were deflected to the stem of the ionization chamber.