diff --git a/scripts/upgrade b/scripts/upgrade
index 669f3ce..ade8b32 100644
--- a/scripts/upgrade
+++ b/scripts/upgrade
@@ -54,7 +54,7 @@ sudo service ffsync stop
 cd $final_path && sudo make build && sudo ./local/bin/easy_install gunicorn
 
 # Disable swapfile
-if [ -z "$tmp_swap_file" ];
+if [ -z ${tmp_swap_file+x} ];
 then
         sudo swapoff $tmp_swap_file
         sudo rm -f $tmp_swap_file