diff --git a/libs/ardour/instrument_info.cc b/libs/ardour/instrument_info.cc
index e7538a061f..4a1dc96046 100644
--- a/libs/ardour/instrument_info.cc
+++ b/libs/ardour/instrument_info.cc
@@ -49,6 +49,9 @@ InstrumentInfo::~InstrumentInfo ()
 void
 InstrumentInfo::set_external_instrument (const string& model, const string& mode)
 {
+	if (external_instrument_model == model && external_instrument_mode == mode && internal_instrument.expired ()) {
+		return;
+	}
 	external_instrument_model = model;
 	external_instrument_mode = mode;
 	internal_instrument.reset ();
@@ -58,6 +61,7 @@ InstrumentInfo::set_external_instrument (const string& model, const string& mode
 void
 InstrumentInfo::set_internal_instrument (boost::shared_ptr<Processor> p)
 {
+	bool changed = !external_instrument_mode.empty ();
 	external_instrument_mode = "";
 
 	boost::shared_ptr<PluginInsert> pi = boost::dynamic_pointer_cast<PluginInsert>(p);
@@ -67,17 +71,24 @@ InstrumentInfo::set_internal_instrument (boost::shared_ptr<Processor> p)
 		 * InstrumentInfo::get_plugin_patch_name() needs to be overhauled,
 		 * it limits all PluginInsert to generic-midi or only numbers.
 		 */
+		changed |= !internal_instrument.expired ();
+		changed |= external_instrument_model != pi->plugin ()->midnam_model ();
+
 		internal_instrument.reset ();
 		external_instrument_model = pi->plugin ()->midnam_model ();
 		const std::list<std::string> device_modes = MIDI::Name::MidiPatchManager::instance().custom_device_mode_names_by_model (external_instrument_model);
 		if (device_modes.size() > 0) {
+			changed |= external_instrument_mode != device_modes.front();
 			external_instrument_mode = device_modes.front();
 		}
 	} else {
+		changed |= internal_instrument.lock () != p || external_instrument_model != _("Unknown");
 		internal_instrument = p;
-		external_instrument_model = (_("Unknown"));
+		external_instrument_model = _("Unknown");
+	}
+	if (changed) {
+		Changed(); /* EMIT SIGNAL */
 	}
-	Changed(); /* EMIT SIGNAL */
 }
 
 string