  We perform the first one-loop electroweak corrections for $2 \to 3$ processes
for dark matter annihilation. These are the dominant processes that enter the
computation of the relic density for the low mass region of the inert doublet
model (IDM) when annihilations to two on-shell vector bosons are closed. The
impact of the one-loop corrections are important as they involve, through
rescattering effects, not only a dependence on the parameter controlling the
dark sector, not present if a calculation at tree-level is conducted, but also
on the renormalisation scale. These combined effects should be taken into
account in analyses based on tree-level cross-sections of the relic density
calculations, as a theoretical uncertainty which we find to be much larger than
the cursory $\pm 10\%$ uncertainty that is routinely assumed, independently of
the model parameters.
