diff --git a/src/Map/RequestTraderMap.php b/src/Map/RequestTraderMap.php
index 84fdc68..2d760ba 100644
--- a/src/Map/RequestTraderMap.php
+++ b/src/Map/RequestTraderMap.php
@@ -112,7 +112,7 @@ function buy(array $data){
                         $map['sz']=$data['_number'] ?? 0;
                     }else{
                         $map['ordType']='market';
-                        $map['sz']=$data['_price'] ?? 0;
+                        $map['sz']=$data['_number'] ?? 0;
                     }
 
                     switch ($this->platform){