  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 Dbar0-D*0 scattering length in the C=+1 channel
to next-to-leading order in 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.
