  We study the quantum stabilization of a cosmic string by a heavy fermion
doublet in a reduced version of the standard model. We show that charged
strings, obtained by populating fermionic bound state levels, become stable if
the electro--weak bosons are coupled to a fermion that is less than twice as
heavy as the top quark. This result suggests that extraordinarily large fermion
masses or unrealistic couplings are not required to bind a cosmic string in the
standard model. Numerically we find the most favorable string profile to be a
simple "trough" in the Higgs vev of radius $\approx 10^{-18}\,\mathrm{m}$. The
vacuum remains stable in our model, because neutral strings are not
energetically favored.
