diff --git a/tmp/post_upgrade_command.php b/tmp/post_upgrade_command.php
index c4a135767..a33dbb617 100755
--- a/tmp/post_upgrade_command.php
+++ b/tmp/post_upgrade_command.php
@@ -14,7 +14,7 @@
 	}
 
 	$newslicedir = "";
-	if ($argv[1] != "")
+	if (isset($argv[1]) && $argv[1] != "")
 		$newslicedir = '/tmp/' . $argv[1];
 
 	if($g['enableserial_force'] || file_exists("{$newslicedir}/enableserial_force")) {