diff --git a/include/libtorrent/upnp.hpp b/include/libtorrent/upnp.hpp
index 7b4559dd91e..47a3b79618c 100644
--- a/include/libtorrent/upnp.hpp
+++ b/include/libtorrent/upnp.hpp
@@ -280,7 +280,7 @@ struct TORRENT_EXTRA_EXPORT upnp final
 		// the url to the WANIP or WANPPP interface
 		std::string control_url;
 		// either the WANIP namespace or the WANPPP namespace
-		char const* service_namespace = nullptr;
+		std::string service_namespace;
 
 		std::vector<mapping_t> mapping;
 
diff --git a/src/upnp.cpp b/src/upnp.cpp
index 220edd3ca5b..6934f27848b 100644
--- a/src/upnp.cpp
+++ b/src/upnp.cpp
@@ -225,7 +225,7 @@ int upnp::add_mapping(portmap_protocol const p, int const external_port
 		m.external_port = external_port;
 		m.local_port = local_port;
 
-		if (d.service_namespace) update_map(d, mapping_index);
+		if (!d.service_namespace.empty()) update_map(d, mapping_index);
 	}
 
 	return mapping_index;
@@ -255,7 +255,7 @@ void upnp::delete_mapping(int mapping)
 		TORRENT_ASSERT(mapping < int(d.mapping.size()));
 		d.mapping[mapping].act = mapping_t::action::del;
 
-		if (d.service_namespace) update_map(d, mapping);
+		if (!d.service_namespace.empty()) update_map(d, mapping);
 	}
 }
 
@@ -699,7 +699,7 @@ void upnp::post(upnp::rootdevice const& d, char const* soap
 		"Soapaction: \"%s#%s\"\r\n\r\n"
 		"%s"
 		, d.path.c_str(), d.hostname.c_str(), d.port
-		, int(strlen(soap)), d.service_namespace, soap_action
+		, int(strlen(soap)), d.service_namespace.c_str(), soap_action
 		, soap);
 
 	d.upnp_connection->m_sendbuffer = header;
@@ -743,7 +743,7 @@ void upnp::create_port_mapping(http_connection& c, rootdevice& d, int i)
 		"<NewPortMappingDescription>%s at %s:%d</NewPortMappingDescription>"
 		"<NewLeaseDuration>%u</NewLeaseDuration>"
 		"</u:%s></s:Body></s:Envelope>"
-		, soap_action, d.service_namespace, d.mapping[i].external_port
+		, soap_action, d.service_namespace.c_str(), d.mapping[i].external_port
 		, (d.mapping[i].protocol == portmap_protocol::udp ? "UDP" : "TCP")
 		, d.mapping[i].local_port
 		, local_endpoint.c_str()
@@ -795,7 +795,7 @@ void upnp::update_map(rootdevice& d, int i)
 	}
 
 	TORRENT_ASSERT(!d.upnp_connection);
-	TORRENT_ASSERT(d.service_namespace);
+	TORRENT_ASSERT(!d.service_namespace.empty());
 
 #ifndef TORRENT_DISABLE_LOGGING
 	log("connecting to %s", d.hostname.c_str());
@@ -852,6 +852,8 @@ void upnp::delete_port_mapping(rootdevice& d, int i)
 
 	char const* soap_action = "DeletePortMapping";
 
+	TORRENT_ASSERT(!d.service_namespace.empty());
+
 	char soap[2048];
 	error_code ec;
 	std::snprintf(soap, sizeof(soap), "<?xml version=\"1.0\"?>\n"
@@ -862,7 +864,7 @@ void upnp::delete_port_mapping(rootdevice& d, int i)
 		"<NewExternalPort>%u</NewExternalPort>"
 		"<NewProtocol>%s</NewProtocol>"
 		"</u:%s></s:Body></s:Envelope>"
-		, soap_action, d.service_namespace
+		, soap_action, d.service_namespace.c_str()
 		, d.mapping[i].external_port
 		, (d.mapping[i].protocol == portmap_protocol::udp ? "UDP" : "TCP")
 		, soap_action);
@@ -996,9 +998,10 @@ void upnp::on_upnp_xml(error_code const& e
 		d.disabled = true;
 		return;
 	}
-	static std::string service_type;
-	service_type.swap(s.service_type);
-	d.service_namespace = service_type.c_str();
+	d.service_namespace = s.service_type;
+
+	TORRENT_ASSERT(!d.service_namespace.empty());
+
 	if (!s.model.empty()) m_model = s.model;
 
 	if (!s.url_base.empty() && s.control_url.substr(0, 7) != "http://")
@@ -1029,7 +1032,7 @@ void upnp::on_upnp_xml(error_code const& e
 	{
 		log("found control URL: %s namespace %s "
 			"urlbase: %s in response from %s"
-			, d.control_url.c_str(), d.service_namespace
+			, d.control_url.c_str(), d.service_namespace.c_str()
 			, s.url_base.c_str(), d.url.c_str());
 	}
 #endif
@@ -1077,6 +1080,8 @@ void upnp::get_ip_address(rootdevice& d)
 
 	char const* soap_action = "GetExternalIPAddress";
 
+	TORRENT_ASSERT(!d.service_namespace.empty());
+
 	char soap[2048];
 	error_code ec;
 	std::snprintf(soap, sizeof(soap), "<?xml version=\"1.0\"?>\n"
@@ -1084,7 +1089,7 @@ void upnp::get_ip_address(rootdevice& d)
 		"s:encodingStyle=\"http://schemas.xmlsoap.org/soap/encoding/\">"
 		"<s:Body><u:%s xmlns:u=\"%s\">"
 		"</u:%s></s:Body></s:Envelope>"
-		, soap_action, d.service_namespace
+		, soap_action, d.service_namespace.c_str()
 		, soap_action);
 
 	post(d, soap, soap_action);