  The influence of local moment magnetism on the boron isotope effect of T$_c$
was studied on single crystals of ErNi$_2$B$_2$C. Values of the partial isotope
effect exponent of $\alpha_B$=0.10$\pm$0.02 and $\alpha_B$=0.10$\pm$0.04 were
obtained based on two different criteria applied to extract $T_c$. No
significant change in the partial isotope effect exponent compared to the ones
obtained for LuNi$_2$B$_2$C was observed. Based on this result we conclude that
pair-breaking due to the Er local magnetic moment appears to have no detectable
influence on boron isotope effect of T$_c$.
