diff --git a/http/http_connection.hpp b/http/http_connection.hpp
index 2139602..7b66ac8 100644
--- a/http/http_connection.hpp
+++ b/http/http_connection.hpp
@@ -602,7 +602,7 @@
 
         std::weak_ptr<Connection<Adaptor, Handler>> weakSelf = weak_from_this();
         timer.expires_after(timeout);
-        timer.async_wait([weakSelf](const boost::system::error_code ec) {
+        timer.async_wait([weakSelf](const boost::system::error_code& ec) {
             // Note, we are ignoring other types of errors here;  If the timer
             // failed for any reason, we should still close the connection
             std::shared_ptr<Connection<Adaptor, Handler>> self =