diff --git a/libs/ardour/ardour/plugin_insert.h b/libs/ardour/ardour/plugin_insert.h
index d1fa7e951e..f15967640b 100644
--- a/libs/ardour/ardour/plugin_insert.h
+++ b/libs/ardour/ardour/plugin_insert.h
@@ -440,6 +440,8 @@ private:
 
 	PBD::TimingStats _timing_stats;
 	volatile gint _stat_reset;
+
+	volatile gint _flush;
 };
 
 } // namespace ARDOUR
diff --git a/libs/ardour/plugin_insert.cc b/libs/ardour/plugin_insert.cc
index 9aab3e9f18..ebb777da2d 100644
--- a/libs/ardour/plugin_insert.cc
+++ b/libs/ardour/plugin_insert.cc
@@ -91,6 +91,7 @@ PluginInsert::PluginInsert (Session& s, boost::shared_ptr<Plugin> plug)
 	, _bypass_port (UINT32_MAX)
 	, _inverted_bypass_enable (false)
 	, _stat_reset (0)
+	, _flush (0)
 {
 	/* the first is the master */
 
@@ -714,9 +715,7 @@ PluginInsert::deactivate ()
 void
 PluginInsert::flush ()
 {
-	for (vector<boost::shared_ptr<Plugin> >::iterator i = _plugins.begin(); i != _plugins.end(); ++i) {
-		(*i)->flush ();
-	}
+	g_atomic_int_set (&_flush, 1);
 }
 
 void
@@ -1269,6 +1268,12 @@ PluginInsert::run (BufferSet& bufs, samplepos_t start_sample, samplepos_t end_sa
 		_timing_stats.reset ();
 	}
 
+	if (g_atomic_int_compare_and_exchange (&_flush, 1, 0)) {
+		for (Plugins::iterator i = _plugins.begin(); i != _plugins.end(); ++i) {
+			(*i)->flush ();
+		}
+	}
+
 	if (_pending_active) {
 #if defined MIXBUS && defined NDEBUG
 		if (!is_channelstrip ()) {