diff --git a/webapp/models/BoxOrder.php b/webapp/models/BoxOrder.php
index 39ce5f66..8a976e6e 100644
--- a/webapp/models/BoxOrder.php
+++ b/webapp/models/BoxOrder.php
@@ -15,7 +15,7 @@ class BoxOrder extends BaseModel {
               array(
                   ':batch_idx' => $batchIdx
               ));
-        return $row && $row['sold_num'] ? $row['sold_num'] : 0;
+        return $row && $row['sold_num'] ? (int)$row['sold_num'] : 0;
     }
 
     public function isBuyed($buyerAddress, $batchIdx)