diff --git a/setup/so-common-functions b/setup/so-common-functions
index ad88fecf0..ab50105c0 100644
--- a/setup/so-common-functions
+++ b/setup/so-common-functions
@@ -31,7 +31,7 @@ filter_unused_nics() {
 calculate_useable_cores() {
 
 	# Calculate reasonable core usage
-	local cores_for_bro=$(( num_cpu_cores/2 - 1 ))
+	local cores_for_bro=$(( (num_cpu_cores/2) - 1 ))
 	local lb_procs_round
 	lb_procs_round=$(printf "%.0f\n" $cores_for_bro)