diff --git a/backup b/backup
index 580111e..a194e05 100755
--- a/backup
+++ b/backup
@@ -35,7 +35,11 @@ my @backup_dirs = map {
 			    = statvfs($_);
 			[ $_, $bsize * $bavail ]
                       } glob("/backup/*/active");
-@backup_dirs = sort { $b->[1] <=> $b->[0] } @backup_dirs;
+@backup_dirs = sort { $b->[1] <=> $a->[1] } @backup_dirs;
+unless (@backup_dirs) {
+    $ca->log(0, "no backup directory found");
+    exit(1);
+}
 $ca->basedir($backup_dirs[0][0]);
 
 $ca->run();