diff --git a/gtk2_ardour/processor_box.cc b/gtk2_ardour/processor_box.cc
index 514d7ede13..e1d65404d7 100644
--- a/gtk2_ardour/processor_box.cc
+++ b/gtk2_ardour/processor_box.cc
@@ -1984,6 +1984,7 @@ ProcessorBox::ProcessorBox (ARDOUR::Session* sess, std::function<PluginSelector*
 	processor_display.Reordered.connect (sigc::mem_fun (*this, &ProcessorBox::reordered));
 	processor_display.DropFromAnotherBox.connect (sigc::mem_fun (*this, &ProcessorBox::object_drop));
 	processor_display.DropFromExternal.connect (sigc::mem_fun (*this, &ProcessorBox::plugin_drop));
+	processor_display.DragRefuse.connect (sigc::mem_fun (*this, &ProcessorBox::drag_refuse));
 
 	processor_scroller.show ();
 	processor_display.show ();
@@ -2151,6 +2152,13 @@ not match the configuration of this track.");
 	}
 }
 
+bool
+ProcessorBox::drag_refuse (DnDVBox<ProcessorEntry>* source, ProcessorEntry*)
+{
+	ProcessorBox* other = reinterpret_cast<ProcessorBox*> (source->get_data ("processorbox"));
+	return (other && other->_route == _route);
+}
+
 void
 ProcessorBox::object_drop (DnDVBox<ProcessorEntry>* source, ProcessorEntry* position, Glib::RefPtr<Gdk::DragContext> const & context)
 {
diff --git a/gtk2_ardour/processor_box.h b/gtk2_ardour/processor_box.h
index 1391a99e6c..bc250745fc 100644
--- a/gtk2_ardour/processor_box.h
+++ b/gtk2_ardour/processor_box.h
@@ -523,6 +523,7 @@ private:
 
 	void plugin_drop (Gtk::SelectionData const &, ProcessorEntry* position, Glib::RefPtr<Gdk::DragContext> const & context);
 	void object_drop (Gtkmm2ext::DnDVBox<ProcessorEntry> *, ProcessorEntry *, Glib::RefPtr<Gdk::DragContext> const &);
+	bool drag_refuse (Gtkmm2ext::DnDVBox<ProcessorEntry> *, ProcessorEntry *);
 
 	Width _width;
 	bool  _redisplay_pending;