diff --git a/2meet-data-optimizer-bookings-addon.php b/2meet-data-optimizer-bookings-addon.php
index c0e5618..98d4e94 100644
--- a/2meet-data-optimizer-bookings-addon.php
+++ b/2meet-data-optimizer-bookings-addon.php
@@ -29,6 +29,7 @@ define( 'TMDO_BOOKINGS_FILE', __FILE__ );
 
 require_once TMDO_BOOKINGS_PATH . 'includes/class-tmdo-bookings-bootstrap.php';
 
+require_once TMDO_BOOKINGS_PATH . 'includes/back-compat-aliases.php';
 /**
  * Phase 4 任務：完成本 AddOn 的 includes/ 實作。
  *
diff --git a/includes/back-compat-aliases.php b/includes/back-compat-aliases.php
new file mode 100644
index 0000000..fe67bec
--- /dev/null
+++ b/includes/back-compat-aliases.php
@@ -0,0 +1,31 @@
+<?php
+/**
+ * Backward-compat class aliases for the bookings AddOn.
+ *
+ * Sister plugins and third-party code may still reference the WPDO_* class
+ * names from wp-data-optimizer. The core plugin aliases its own classes in
+ * class-tmdo-back-compat.php, but it runs before AddOns load (plugins_loaded:4
+ * vs :6), so each AddOn must alias its own classes here.
+ *
+ * @package TMDO
+ */
+
+if ( ! defined( 'ABSPATH' ) ) {
+	exit;
+}
+
+add_action(
+	'plugins_loaded',
+	static function () {
+		$aliases = array(
+			'TMDO_Bookings' => 'WPDO_Bookings',
+			'TMDO_Bookings_Bootstrap' => 'WPDO_Bookings_Bootstrap',
+		);
+		foreach ( $aliases as $tmdo_class => $wpdo_alias ) {
+			if ( class_exists( $tmdo_class, false ) && ! class_exists( $wpdo_alias, false ) ) {
+				class_alias( $tmdo_class, $wpdo_alias );
+			}
+		}
+	},
+	7
+);