diff --git a/src/session_impl.cpp b/src/session_impl.cpp
index 9b3e667a5..3c8625fef 100755
--- a/src/session_impl.cpp
+++ b/src/session_impl.cpp
@@ -2279,6 +2279,8 @@ namespace detail
 
 		INVARIANT_CHECK;
 
+		if (m_lsd) return;
+
 		m_lsd = new lsd(m_io_service
 			, m_listen_interface.address()
 			, bind(&session_impl::on_lsd_peer, this, _1, _2));
@@ -2290,6 +2292,8 @@ namespace detail
 
 		INVARIANT_CHECK;
 
+		if (m_natpmp) return;
+
 		m_natpmp = new natpmp(m_io_service
 			, m_listen_interface.address()
 			, bind(&session_impl::on_port_mapping
@@ -2308,6 +2312,8 @@ namespace detail
 
 		INVARIANT_CHECK;
 
+		if (m_upnp) return;
+
 		m_upnp = new upnp(m_io_service, m_half_open
 			, m_listen_interface.address()
 			, m_settings.user_agent