diff --git a/lib/common/multipart.js b/lib/common/multipart.js
index f9a798666..75839f30c 100644
--- a/lib/common/multipart.js
+++ b/lib/common/multipart.js
@@ -236,10 +236,7 @@ proto._uploadPart = async function _uploadPart(name, uploadId, partNo, data, opt
   const opt = {};
   copy(options).to(opt);
   opt.headers = opt.headers || {};
-  opt.headers = {
-    ...opt.headers,
-    'Content-Length': data.size
-  };
+  copy({ 'Content-Length': data.size }).to(opt.headers);
 
   // Uploading shards does not require x-oss server side encryption
   opt.headers = omit(opt.headers, ['x-oss-server-side-encryption']);