diff --git a/usr/sbin/tupper b/usr/sbin/tupper
index 8f7a91e..081b00a 100755
--- a/usr/sbin/tupper
+++ b/usr/sbin/tupper
@@ -13,7 +13,7 @@ fi
 source "$CONF"
 
 # Check if required variables are set
-if [ "$SSH_URI$SSH_PASS$TARGET" = "" ]; then
+if [ "$SSH_URI" = "" ] || [ "$SSH_PASS" = "" ] || [ "$TARGET" = "" ]; then
 	echo "Config file $CONF must contain SSH_URI, SSH_PASS and TARGET" 1>&2
 	exit 1
 fi