  Using a reweighting technique combined with a low-mode truncation of the
fermionic determinant, we estimate the quark-mass dependence of the QCD
topological susceptibility with overlap fermions. In contrast to previous
lattice simulations which all used non-chiral fermions, our results appear to
be consistent with the simple continuum model of D\"urr. This indicates that at
current lattice spacings the use of the index theorem might not be justified
and the fermionic definition of the charge might be needed.
