Suppose $\mathcal C$ is a preadditive, Karoubi category with a zero object. What further assumptions on $\mathcal C$ are required to ensure that the endomorphism ring of an indecomposable object is a local?

By an object $X$ being indecomposable, I mean that in any biproduct decomposition $X \cong X_1 \oplus X_2$, one has $X_i \cong 0$ for some $i=1,2$.

Thanks for your help.