diff --git a/backup.nix b/backup.nix
index d3a473a..73d3084 100644
--- a/backup.nix
+++ b/backup.nix
@@ -4,7 +4,7 @@ let
   user = "misskey-backup";
   group = user;
 
-  # shell script file to be sourced. must have values "bucket" "prefix" and "s3cfg"
+  # shell script file to be sourced. must have values "MISSKEY_BACKUP_BUCKET" "MISSKEY_BACKUP_PREFIX" and "S3CFG"
   backupConfigFile = "/etc/misskey-backup";
   backupScript = pkgs.writeShellApplication {
     name = "misskey-backup";
@@ -16,9 +16,11 @@ let
       coreutils
     ];
 
+    extraShellCheckFlags = [ "-x" "/etc/misskey-backup" ];
+
     text = ''
       source "${backupConfigFile}"
-      pg_dump misskey | gzip | s3cmd put --config "$s3cfg" - "s3://$bucket/$prefix/misskey-pgdump-$(date --iso-8601).sql.gz"
+      pg_dump misskey | gzip | s3cmd put --config "$S3CFG" - "s3://$MISSKEY_BACKUP_BUCKET/$MISSKEY_BACKUP_PREFIX/misskey-pgdump-$(date --iso-8601).sql.gz"
     '';
   };
 in {