  The Hawking evaporation of primordial black holes (PBH) reheats the Universe
locally, forming hot spots that survive throughout their lifetime. We propose
to use the temperature profile of such hot spots to calculate the decay rate of
metastable vacua in cosmology, avoiding inconsistencies inherent to the
Hartle-Hawking or Unruh vacuum. We apply our formalism to the case of the
electroweak vacuum stability and find that a PBH energy fraction $\beta >
7\times 10^{-80} (M/g)^{3/2}$ is ruled out for black holes with masses $0.8 g <
M < 10^{15} g$.
