diff --git a/build.sh b/build.sh
index b59834f..c6d9699 100755
--- a/build.sh
+++ b/build.sh
@@ -42,7 +42,8 @@ case ${1} in
 *)	exec cat build.usage; ;;
 esac; shift; done;
 
-if [ -e /proc/cpuinfo ]; then
+if [ -z "${BUILD_CPUS}" ]	\
+&& [ -e /proc/cpuinfo ]; then
 	BUILD_CPUS=$(awk '/^processor/{cpus++} END{print cpus}' /proc/cpuinfo);
 fi;