diff --git a/FastDFS/Storage/UPLOAD_FILE.cs b/FastDFS/Storage/UPLOAD_FILE.cs
index 8bd930d..b5e3139 100644
--- a/FastDFS/Storage/UPLOAD_FILE.cs
+++ b/FastDFS/Storage/UPLOAD_FILE.cs
@@ -61,7 +61,8 @@ public override FDFSRequest GetRequest(params object[] paramList)
             IPEndPoint endPoint = (IPEndPoint)paramList[0];
             
             byte storePathIndex = (byte)paramList[1];
-            long fileSize = (long)paramList[2];
+            //long fileSize = (long)paramList[2];  //会引发"指定的转换无效"
+            long fileSize = Convert.ToInt64(paramList[2]);
             string ext = (string)paramList[3];
             
             Stream stream = paramList[4] as Stream;