diff --git a/rebuild.sh b/rebuild.sh
index 991ce6d..efeec92 100755
--- a/rebuild.sh
+++ b/rebuild.sh
@@ -1,7 +1,7 @@
 #!/usr/bin/env bash
 set -x
 
-if [ "x$1" = "x" ]
+if [ -z "$1" ]
 then
   h="$(hostname -s)"
 else