  We study the spectral gap of the Wilson--Dirac operator in two-flavour
lattice QCD as a function of the lattice spacing $a$, the space-time volume $V$
and the current-quark mass $m$. It turns out that the median of the probability
distribution of the gap scales proportionally to $m$ and that its width is
practically equal to $a/\sqrt{V}$. In particular, numerical simulations are
safe from accidental zero modes in the large-volume regime of QCD.
