diff --git a/src/xclient_zmq_impl.cpp b/src/xclient_zmq_impl.cpp
index 269c0ac..896defb 100644
--- a/src/xclient_zmq_impl.cpp
+++ b/src/xclient_zmq_impl.cpp
@@ -15,6 +15,11 @@
 
 namespace xeus
 {
+    namespace
+    {
+        constexpr std::size_t max_retry = 3;
+        constexpr long heartbeat_timeout = std::chrono::milliseconds(90).count();
+    }
 
     xclient_zmq_impl::xclient_zmq_impl(zmq::context_t& context,
                                     const xeus::xconfiguration& config,
@@ -23,7 +28,7 @@ namespace xeus
         , m_shell_client(context, config.m_transport, config.m_ip, config.m_shell_port)
         , m_control_client(context, config.m_transport, config.m_ip, config.m_control_port)
         , m_iopub_client(context, config)
-        , m_heartbeat_client(context, config, m_max_retry, m_heartbeat_timeout)
+        , m_heartbeat_client(context, config, max_retry, heartbeat_timeout)
         , p_messenger(context)
         , m_error_handler(eh)
     {
@@ -195,4 +200,4 @@ namespace xeus
         return xzmq_serializer::deserialize(wire_msg, *p_auth);
     }
 
-}
\ No newline at end of file
+}
diff --git a/src/xclient_zmq_impl.hpp b/src/xclient_zmq_impl.hpp
index 9854de5..b52aa80 100644
--- a/src/xclient_zmq_impl.hpp
+++ b/src/xclient_zmq_impl.hpp
@@ -93,9 +93,6 @@ namespace xeus
         xiopub_client m_iopub_client;
         xheartbeat_client m_heartbeat_client;
 
-        const std::size_t m_max_retry = 3;
-        const long m_heartbeat_timeout = std::chrono::milliseconds(90).count();
-
         xclient_messenger p_messenger;
 
         nl::json::error_handler_t m_error_handler;
@@ -112,4 +109,4 @@ namespace xeus
     };
 }
 
-#endif
\ No newline at end of file
+#endif