  We present results for the interaction of two kaons at maximal isospin. The
calculation is based on 2+1+1 flavour gauge configurations generated by the ETM
Collaboration (ETMC) featuring pion masses ranging from about 230 MeV to 450
MeV at three values of the lattice spacing. The elastic scattering length
$a_0^{I=1}$ is calculated at several values of the bare strange quark and light
quark masses. We find $M_K a_0 =-0.397(11)(_{-8}^{+0})$ as the result of a
chiral and continuum extrapolation to the physical point. This number is
compared to other lattice results.
