diff --git a/daily-build b/daily-build
index f1c0c6c49..27ce6ae3d 100755
--- a/daily-build
+++ b/daily-build
@@ -1,13 +1,13 @@
 #!/bin/sh -e
 
 # Set these in the environment to override.
-if [ -n "$HOST" ]; then
+if [ -z "$HOST" ]; then
 	HOST=people.debian.org
 fi
-if [ -n "$BASEDIR" ]; then
+if [ -z "$BASEDIR" ]; then
 	BASEDIR=public_html/d-i/images
 fi
-if [ -n "$DIR" ]; then
+if [ -z "$DIR" ]; then
 	DIR=`date +%Y-%m-%d`
 fi