diff --git a/run b/run
index f879612..b607194 100755
--- a/run
+++ b/run
@@ -1,11 +1,12 @@
 #!/usr/bin/env bash
 set -e
+export target_os="${target_os:=$1}"
 
-if [ "$#" -ne "1" ]; then
+if [ "$target_os" = "" ]; then
     echo "Usage: $0 <linux/openbsd>"
     exit 1
 fi
-export target_os="$1"
+
 case "$target_os" in
     linux)
         echo "* Compiling: linux ..."