  Observations of the cosmic microwave background constrain the abundance of
primordial black holes, as these would accrete gas and inject energy into the
cosmological medium. We have revisited these constraints, taking into account
the local heating and ionisation of the gas around the black holes. While
constraints for \textit{naked} black holes are not significantly affected,
bounds including dark matter mini-halos are drastically relaxed. This result
suggests that previous analysis may have significantly overestimated the role
of dark matter mini-halos in boosting the accretion rates.
