  We consider Dirichlet-to-Neumann operators associated to $\Delta+q$ on a
Lipschitz domain in a smooth manifold, where $q$ is an $L^{\infty}$ potential.
We prove a Courant-type bound for the nodal count of the extensions $u_k$ of
the $k$th Dirichlet-to-Neumann eigenfunctions $\phi_k$ to the interior
satisfying $(\Delta+q)u_k=0$. The classical Courant nodal domain theorem is
known to hold for Steklov eigenfunctions, which are the harmonic extension of
the Dirichlet-to-Neumann eigenfunctions associated to $\Delta$. Our result
extends it to a larger family of Dirichlet-to-Neumann operators. Our proof
makes use of the duality between the Steklov and Robin problems.
