In the framework of the minimal cosmological standard model, the $\Lambda$CDM model, the Dark Matter density is now known with an error of a few percent; this error is expected to shrink even further once PLANCK data are analyzed. Matching this precision by theoretical calculations implies that at least leading radiative corrections to the annihilation cross section of the dark matter particles have to be included. Here we compute one kind of large corrections in the context of the minimal supersymmetric extension of the Standard Model: corrections associated with two-point function corrections on chargino and neutralino lines. These can be described by effective chargino/neutralino-fermion-sfermion and chargino/neutralino-chargino/neutralino-Higgs couplings. We also employ one-loop corrected chargino and neutralino masses, using a recently developed version of the on-shell renormalization scheme. The resulting correction to the predicted Dark Matter density depends strongly on parameter space, but can easily reach 3%.