  We present an updated and improved global fit analysis of precision and
flavor observables so as to derive constraints on deviations from unitarity in
the leptonic mixing matrix. We focus on the case in which these deviations are
sourced by heavy neutrinos, such that our results can also be interpreted as
bounds on their mixing with the active flavors. Our analysis is motivated by
new results on key observables, such as $M_W$, $|V_{ud}|$ and
$\Gamma_{\text{inv}}$.
