The effect of a static helical magnetic field on the nonlinear growth of the neoclassical tearing mode (NTM) is investigated. The NTM is found to be stabilized by an externally applied helical field of a different helicity if the field magnitude is sufficiently large, suggesting a very simple method for stabilizing the NTM. The mechanism responsible for this stabilization is the decreased fundamental harmonic pressure perturbation of the NTM in the presence of the helical field.