diff --git a/README.md b/README.md
index 301d297..6eb5ae3 100644
--- a/README.md
+++ b/README.md
@@ -28,7 +28,7 @@ This script is used to reinstall the Linux OS of a KVM-based VPS or a Hyper-V vi
  - `--mirror-protocol http` (`http`/`https`/`ftp`)
  - `--mirror-host deb.debian.org`
  - `--mirror-directory /debian`
- - `--security-repository http://security.debian.org/debian-security`
+ - `--security-repository http://security.debian.org/debian-security` Magic value: `'mirror' = <mirror-protocol>://<mirror-host>/<mirror-directory>/../debian-security`
  - `--skip-account-setup`
  - `--username debian`
  - `--password`
diff --git a/debi.sh b/debi.sh
index 71a0e7f..baf84cf 100755
--- a/debi.sh
+++ b/debi.sh
@@ -68,13 +68,13 @@ while [ $# -gt 0 ]; do
                     mirror_protocol=https
                     mirror_host=mirrors.aliyun.com
                     ntp=ntp.aliyun.com
-                    security_repository=true
+                    security_repository=mirror
                     ;;
                 cloud)
                     dns='1.1.1.1 1.0.0.1'
                     mirror_protocol=https
                     mirror_host=deb.debian.org
-                    security_repository=true
+                    security_repository=mirror
                     ;;
                 *)
                     _err "No such preset $2"
@@ -463,7 +463,7 @@ EOF
 [ "$install_recommends" = false ] && echo "d-i base-installer/install-recommends boolean $install_recommends" | $save_preseed
 [ -n "$kernel" ] && echo "d-i base-installer/kernel/image string $kernel" | $save_preseed
 
-[ "$security_repository" = true ] && security_repository=$mirror_protocol://$mirror_host${mirror_directory%/*}/debian-security
+[ "$security_repository" = mirror ] && security_repository=$mirror_protocol://$mirror_host${mirror_directory%/*}/debian-security
 
 $save_preseed << EOF