  Fessler and Gutierrez \cite{Fe,Gu} proved that if a non-singular planar map
has Jacobian matrix without eigenvalues in $(0,+\infty)$, then it is injective.
We prove that the same holds replacing $(0,+\infty)$ with any unbounded curve
disconnecting the upper (lower) complex half-plane. Additionally we prove that
a Jacobian map $(P,Q)$ is injective if $P_x + Q_y$ is not a surjective
function.
