diff --git a/http/http_client.hpp b/http/http_client.hpp
index c902e1a..fff261f 100644
--- a/http/http_client.hpp
+++ b/http/http_client.hpp
@@ -401,7 +401,7 @@
     }
 
     static void onTimeout(const std::weak_ptr<ConnectionInfo>& weakSelf,
-                          const boost::system::error_code ec)
+                          const boost::system::error_code& ec)
     {
         if (ec == boost::asio::error::operation_aborted)
         {