diff --git a/libs/ardour/ardour/plugin.h b/libs/ardour/ardour/plugin.h
index f74341d9ad..3144302e43 100644
--- a/libs/ardour/ardour/plugin.h
+++ b/libs/ardour/ardour/plugin.h
@@ -106,8 +106,6 @@ public:
 		activate ();
 	}
 
-	virtual void drop_references () {}
-
 	virtual std::set<Evoral::Parameter> automatable () const                   = 0;
 	virtual std::string                 describe_parameter (Evoral::Parameter) = 0;
 	virtual std::string                 state_node_name () const               = 0;
diff --git a/libs/ardour/luaproc.cc b/libs/ardour/luaproc.cc
index 42f57d9f59..7e77af8b88 100644
--- a/libs/ardour/luaproc.cc
+++ b/libs/ardour/luaproc.cc
@@ -186,6 +186,7 @@ void
 LuaProc::drop_references ()
 {
 	lua.collect_garbage ();
+	Plugin::drop_references ();
 }
 
 boost::weak_ptr<Route>
diff --git a/libs/ardour/plugin_insert.cc b/libs/ardour/plugin_insert.cc
index 9bf723a50b..131892df5e 100644
--- a/libs/ardour/plugin_insert.cc
+++ b/libs/ardour/plugin_insert.cc
@@ -114,6 +114,9 @@ PluginInsert::~PluginInsert ()
 void
 PluginInsert::drop_references ()
 {
+	if (!_impulseAnalysisPlugin.expired()) {
+		_impulseAnalysisPlugin.lock()->drop_references ();
+	}
 	for (Plugins::iterator i = _plugins.begin(); i != _plugins.end(); ++i) {
 		(*i)->drop_references ();
 	}
@@ -173,6 +176,7 @@ PluginInsert::set_count (uint32_t num)
 	} else if (num < _plugins.size()) {
 		uint32_t diff = _plugins.size() - num;
 		for (uint32_t n= 0; n < diff; ++n) {
+			_plugins.back()->drop_references ();
 			_plugins.pop_back();
 		}
 		PluginConfigChanged (); /* EMIT SIGNAL */