diff --git a/libs/ardour/ardour/port_insert.h b/libs/ardour/ardour/port_insert.h
index fee1f4694c..0b1b3fbc00 100644
--- a/libs/ardour/ardour/port_insert.h
+++ b/libs/ardour/ardour/port_insert.h
@@ -26,6 +26,7 @@
 
 #include "ardour/ardour.h"
 #include "ardour/io_processor.h"
+#include "ardour/delivery.h"
 #include "ardour/libardour_visibility.h"
 #include "ardour/types.h"
 
@@ -54,6 +55,10 @@ class LIBARDOUR_API PortInsert : public IOProcessor
 
 	void run (BufferSet& bufs, framepos_t start_frame, framepos_t end_frame, double speed, pframes_t nframes, bool);
 
+	void flush_buffers (framecnt_t nframes) {
+		_out->flush_buffers (nframes);
+	}
+
 	framecnt_t signal_latency () const;
 
 	bool set_name (const std::string& name);
diff --git a/libs/ardour/route.cc b/libs/ardour/route.cc
index cd670df02e..1e1be37d9f 100644
--- a/libs/ardour/route.cc
+++ b/libs/ardour/route.cc
@@ -3398,6 +3398,11 @@ Route::flush_processor_buffers_locked (framecnt_t nframes)
 		boost::shared_ptr<Delivery> d = boost::dynamic_pointer_cast<Delivery> (*i);
 		if (d) {
 			d->flush_buffers (nframes);
+		} else {
+			boost::shared_ptr<PortInsert> p = boost::dynamic_pointer_cast<PortInsert> (*i);
+			if (p) {
+				p->flush_buffers (nframes);
+			}
 		}
 	}
 }