diff --git a/gtk2_ardour/lv2_plugin_ui.cc b/gtk2_ardour/lv2_plugin_ui.cc
index fc09902b5b..45e1a464cf 100644
--- a/gtk2_ardour/lv2_plugin_ui.cc
+++ b/gtk2_ardour/lv2_plugin_ui.cc
@@ -70,7 +70,6 @@ LV2PluginUI::write_from_ui(void*       controller,
 
 		std::shared_ptr<AutomationControl> ac = me->_controllables[port_index];
 
-
 		if (ac) {
 			me->_updates.insert (port_index);
 			ac->set_value(*(const float*)buffer, Controllable::NoGroup);
@@ -239,10 +238,8 @@ LV2PluginUI::queue_port_update()
 {
 	const uint32_t num_ports = _lv2->num_ports();
 	for (uint32_t i = 0; i < num_ports; ++i) {
-		bool     ok;
-		uint32_t port = _lv2->nth_parameter(i, ok);
-		if (ok && _lv2->parameter_is_input (i)) {
-			_updates.insert (port);
+		if (_lv2->parameter_is_control (i) && _lv2->parameter_is_input(i)) {
+			_updates.insert (i);
 		}
 	}
 }
@@ -274,9 +271,7 @@ LV2PluginUI::output_update()
 
 	/* output ports (values set by DSP) need propagating to GUI */
 
-	uint32_t nports = _output_ports.size();
-	for (uint32_t i = 0; i < nports; ++i) {
-		uint32_t index = _output_ports[i];
+	for (auto const& index: _output_ports) {
 		float val = _pib->control_output (index)->get_parameter ();
 
 		if (val != _values_last_sent_to_ui[index]) {
@@ -288,14 +283,14 @@ LV2PluginUI::output_update()
 	}
 
 	/* Input ports marked for update because the control value changed
-	   since the last redisplay.
-	*/
+	 * since the last redisplay.
+	 */
 
-	for (Updates::iterator i = _updates.begin(); i != _updates.end(); ++i) {
-		float val = _controllables[*i]->get_value ();
+	for (auto const& i : _updates) {
+		float val = _controllables[i]->get_value ();
 		/* push current value to the GUI */
-		suil_instance_port_event ((SuilInstance*)_inst, (*i), 4, 0, &val);
-		_values_last_sent_to_ui[(*i)] = val;
+		suil_instance_port_event ((SuilInstance*)_inst, i, 4, 0, &val);
+		_values_last_sent_to_ui[i] = val;
 	}
 
 	_updates.clear ();
@@ -436,15 +431,6 @@ LV2PluginUI::lv2ui_instantiate(const std::string& title)
 
 #define GET_WIDGET(inst) suil_instance_get_widget((SuilInstance*)inst);
 
-	const uint32_t num_ports = _lv2->num_ports();
-	for (uint32_t i = 0; i < num_ports; ++i) {
-		if (_lv2->parameter_is_output(i)
-		    && _lv2->parameter_is_control(i)
-		    && is_update_wanted(i)) {
-			_output_ports.push_back(i);
-		}
-	}
-
 	_external_ui_ptr = NULL;
 	if (!is_external_ui) {
 		GtkWidget* c_widget = (GtkWidget*)GET_WIDGET(_inst);
@@ -465,28 +451,30 @@ LV2PluginUI::lv2ui_instantiate(const std::string& title)
 		_external_ui_ptr = (struct lv2_external_ui*)GET_WIDGET(_inst);
 	}
 
+	const uint32_t num_ports = _lv2->num_ports();
+
 	_values_last_sent_to_ui = new float[num_ports];
 	_controllables.resize(num_ports);
 
 	for (uint32_t i = 0; i < num_ports; ++i) {
-		bool     ok;
-		uint32_t port = _lv2->nth_parameter(i, ok);
-		if (ok) {
-			/* Cache initial value of the parameter, regardless of
-			   whether it is input or output
-			*/
+		if (!_lv2->parameter_is_control (i)) {
+			continue;
+		}
 
-			_values_last_sent_to_ui[port]        = _lv2->get_parameter(port);
-			_controllables[port] = std::dynamic_pointer_cast<ARDOUR::AutomationControl> (
-				_pib->control(Evoral::Parameter(PluginAutomation, 0, port)));
+		/* Cache initial value of the parameter, regardless of whether it is input or output */
 
-			if (_lv2->parameter_is_control(port) && _lv2->parameter_is_input(port)) {
-				if (_controllables[port]) {
-					_controllables[port]->Changed.connect (control_connections, invalidator (*this), boost::bind (&LV2PluginUI::control_changed, this, port), gui_context());
-					/* queue for first update ("push") to GUI */
-					_updates.insert (port);
-				}
-			}
+		_values_last_sent_to_ui[i] = _lv2->get_parameter(i);
+		_controllables[i] = std::dynamic_pointer_cast<ARDOUR::AutomationControl> (_pib->control(Evoral::Parameter(PluginAutomation, 0, i)));
+
+		if (_lv2->parameter_is_input(i)) {
+			assert (_controllables[i]);
+			_controllables[i]->Changed.connect (control_connections, invalidator (*this), boost::bind (&LV2PluginUI::control_changed, this, i), gui_context());
+			/* queue for first update ("push") to GUI */
+			_updates.insert (i);
+		}
+
+		if (_lv2->parameter_is_output(i) && is_update_wanted(i)) {
+			_output_ports.push_back (i);
 		}
 	}
 
diff --git a/gtk2_ardour/lv2_plugin_ui.h b/gtk2_ardour/lv2_plugin_ui.h
index 217148d20d..322b8394d6 100644
--- a/gtk2_ardour/lv2_plugin_ui.h
+++ b/gtk2_ardour/lv2_plugin_ui.h
@@ -80,7 +80,7 @@ private:
 
 	std::shared_ptr<ARDOUR::PlugInsertBase> _pib;
 	std::shared_ptr<ARDOUR::LV2Plugin>      _lv2;
-	std::vector<int>                          _output_ports;
+	std::vector<uint32_t>                     _output_ports;
 	sigc::connection                          _screen_update_connection;
 	sigc::connection                          _message_update_connection;
 	Gtk::Widget*                              _gui_widget;