diff --git a/build.sh b/build.sh
index 323b8e4..e9612d3 100755
--- a/build.sh
+++ b/build.sh
@@ -305,7 +305,7 @@ else
 	tar_opts=xzf
 fi
 if [[ "$prefix" = "/" ]]; then fail "Cannot use root (/) as prefix"; fi
-shift $(("$OPTIND" - 1))
+shift $((OPTIND - 1))
 
 case "$1" in
 build)