diff --git a/server_http.hpp b/server_http.hpp
index 0fc5cc2..9f54eef 100644
--- a/server_http.hpp
+++ b/server_http.hpp
@@ -275,7 +275,7 @@ namespace SimpleWeb {
                         try {
                             auto content_length=stoull(it->second);
                             boost::asio::async_read(*socket, request->streambuf, 
-                                    boost::asio::transfer_exactly(stoull(it->second)-num_additional_bytes),
+                                    boost::asio::transfer_exactly(content_length-num_additional_bytes),
                                     [this, socket, request, timer]
                                     (const boost::system::error_code& ec, size_t /*bytes_transferred*/) {
                                 if(timeout_content>0)