diff --git a/builder.sh b/builder.sh
index aca8ec1d349af75d81631402eb2c37291384d514..94261be42682ebfe04c1b8ca74bdb1a43e910953 100755
--- a/builder.sh
+++ b/builder.sh
@@ -57,7 +57,9 @@ DEBUG="V=s"
 PRIO=0
 
 # how parallel do you want to build?
-J=10
+if [ -z "${J}" ]; then
+	J=10
+fi
 
 # prepare site.conf from template
 if [ -f site/site.conf ]; then