diff --git a/tools/appliance/build.sh b/tools/appliance/build.sh
index d18faaf7ce6..f1ee4a64b40 100644
--- a/tools/appliance/build.sh
+++ b/tools/appliance/build.sh
@@ -18,7 +18,7 @@
 
 set -x
 
-if [ "$1"!="" ]
+if [ ! -z "$1" ]
 then
   appliance="$1"
 else