Any smooth arc $\Gamma $ in $\mathbb {C}^n$ is polynomially convex and one can approximate any continuous function on $\Gamma $ by polynomials. Our goal is to show that if $n \geq 2$, under a global biholomorphic change of variables, an arc can always be “straightened” (approximatly mapped to a line segment). This makes polynomial convexity and polynomial approximation trivial, unfortunately we need to use polynomial convexity in our proof.