  Catalysis of nucleon decay in white dwarfs is used to constrain the abundance
of magnetic monopoles arising from Grand Unified Theories. Recent discoveries
of the dimmest white dwarf ever observed, WD 1136-286 with $L = 10^{-4.94}
L_{\odot}$, place limits on the monopole flux. An abundance of monopoles
greater than the new bound would heat this star to a luminosity higher than
what is observed. The new bound is $(F/$cm $^{-2}$ s$^{-1}$ sr$^{-1}$) $(\sigma
\upsilon/10^{-28} cm^2) < 1.3 \times 10^{-20} (\upsilon/10^{-3}c)^2$, where
$\upsilon $ is the monopole velocity. The limit is improved by including the
monopoles captured by the main-sequence progenitor of the white dwarf: $(F/$cm
$^{-2}$ s$^{-1}$ sr$^{-1}$) $(\sigma \upsilon /10^{-28} cm^2) < 3.5(26) \times
10^{-21}$ for $10^{17}$ ($10^{16}$) GeV monopoles. We also note that the
dependence on monopole mass of flux bounds due to catalysis in neutron stars
with main sequence accretion has previously been calculated incorrectly
(previously the bound has been stated as $F (\sigma \upsilon/10^{-28} cm^2) <
10^{-28} $ cm $^{-2}$ s$^{-1}$ sr$^{-1}$). We show that the correct bounds are
somewhat weaker for monopole mass other than $10^{17}$ GeV.
