diff --git a/upyun/upyun.py b/upyun/upyun.py
index 40904b1..0cbd5bd 100644
--- a/upyun/upyun.py
+++ b/upyun/upyun.py
@@ -79,7 +79,7 @@ def put(self, key, value, checksum=False, headers=None):
         if headers is None:
             headers = {}
         headers['Mkdir'] = 'true'
-        if checksum is True:
+        if checksum is True and 'Content-MD5' not in headers:
             headers['Content-MD5'] = self.__make_content_md5(value)
         h = self.__do_http_request('PUT', key, value, headers)
 
@@ -175,6 +175,9 @@ def __make_content_md5(self, value):
         else:
             raise UpYunClientException("object type error")
 
+    def make_content_md5(self, value):
+        return self.__make_content_md5(value)
+
     def __get_meta_headers(self, headers):
         return dict(iter([(k[8:].lower(), v) for k, v in headers
                     if k[:8].lower() == 'x-upyun-']))