  We demonstrate that cation-related localized states strongly perturb the band
structure of $\text{Al}_{1-x}\text{In}_x$N leading to a strong band gap bowing
at low In content. Our first-principles calculations show that In-related
localized states are formed both in the conduction and the valence band in
$\text{Al}_{1-x}\text{In}_x$N for low In composition, $x$, and that these
localized states dominate the evolution of the band structure with increasing
$x$. Therefore, the commonly used assumption of a single
composition-independent bowing parameter breaks down when describing the
evolution both of the conduction and of the valence band edge in
$\text{Al}_{1-x}\text{In}_x$N.
