diff --git a/make_image.sh b/make_image.sh
index cfef136..81dd97c 100755
--- a/make_image.sh
+++ b/make_image.sh
@@ -44,7 +44,7 @@
 done
 shift `expr $OPTIND - 1`
 
-if [ ! "$#" -eq "2" -o -n $CHROOTONLY -a -n $IMAGEONLY ]; then
+if [ ! "$#" -eq "2" -o -n "$CHROOTONLY" -a -n "$IMAGEONLY" ]; then
     usage
 fi