diff --git a/libs/ardour/graph.cc b/libs/ardour/graph.cc
index b590f1fff4..0987b979a2 100644
--- a/libs/ardour/graph.cc
+++ b/libs/ardour/graph.cc
@@ -394,7 +394,7 @@ Graph::main_thread()
 
         this->prep();
 
-        if (_graph_empty) {
+        if (_graph_empty && !_quit_threads) {
                 sem_post (&_callback_done_sem);
                 goto again;
         }