Index: libs/ardour/internal_send.cc
===================================================================
--- libs/ardour/internal_send.cc	(revision 11295)
+++ libs/ardour/internal_send.cc	(working copy)
@@ -256,6 +256,7 @@
 		if (!IO::connecting_legal) {
 			IO::ConnectingLegal.connect_same_thread (connect_c, boost::bind (&InternalSend::connect_when_legal, this));
 		} else {
+			Glib::Mutex::Lock lm (AudioEngine::instance()->process_lock ()); // for InternalReturn::add_send	 
 			connect_when_legal ();
 		}
 	}