diff --git a/webapp/controller/ShopController.class.php b/webapp/controller/ShopController.class.php
index d59c0be1..e3168dfc 100644
--- a/webapp/controller/ShopController.class.php
+++ b/webapp/controller/ShopController.class.php
@@ -1282,7 +1282,7 @@ class ShopController extends BaseAuthedController
         $item_id = getReqVal('item_id', 0);
         $meta = mt\Item::get($item_id);
         $box = Bag::find($item_id);
-        error_log('openBlindBox ' . $box . ' ' . $item_id . ' ' . $meta['sub_type']);
+        error_log('openBlindBox ' . json_encode($box) . ' ' . $item_id . ' ' . $meta['sub_type']);
         if (!$box) {
             $this->_rspErr(2, 'item_id is invalid');
             return;