  In this note, we present a fractional version of Haemers' bound on the
Shannon capacity of a graph, which is originally due to Blasiak. This bound is
a common strengthening of both Haemers' bound and the fractional chromatic
number of a graph. We show that this fractional version outperforms any bound
on the Shannon capacity that could be attained through Haemers' bound. We show
also that this bound is multiplicative, unlike Haemers' bound.
