The quark mass dependence of hadrons is an important input for lattice calculations. We investigate the light quark mass dependence of the binding energy of the X(3872) and the D̄0D*0 scattering length in the C =+1 channel to next-to-leading order in an effective field theory for the X (XEFT) where pion interactions are perturbative. At this order, the quark mass dependence is determined by a quark mass-dependent contact interaction in addition to the one-pion exchange. Using naturalness arguments to constrain unknown parameters, we find a moderate sensitivity of the binding energy for quark masses up to twice the physical value while the scattering length is more sensitive. The occurrence of infrared divergences due to on-shell pions in XEFT and their treatment is discussed in detail.