  Instabilities in finite difference codes due to the singularity of spherical
coordinates at the center are studied. In typical Numerical Relativity
applications, standard regularization techniques by themselves do not ensure
long term stability. A proposal to remedy that problem is presented, which
takes advantage of redundant quantities introduced in recent hyperbolic
formulations of Einstein's evolution equations. The results are discussed
through the example case of a boson star, where a significant improvement in
the implementation of boundary conditions is also presented.
