diff --git a/webapp/controller/BagController.class.php b/webapp/controller/BagController.class.php
index 0e30c09e..4d5216fb 100644
--- a/webapp/controller/BagController.class.php
+++ b/webapp/controller/BagController.class.php
@@ -436,6 +436,10 @@ class BagController extends BaseAuthedController {
             $this->_rspErr(1, "item_id error");
             return;
         }
+        if ($itemNum < 1){
+            $this->_rspErr(1, "item_num error");
+            return;
+        }
         if ($itemMeta['type'] != mt\Item::FUNC_TYPE) {
             $this->_rspErr(1, "only supported property");
             return;