diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index ad115d4ae7..1c6b08b95d 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -1205,6 +1205,7 @@ Session::auto_loop_changed (Location* location)
 	}
 
 	last_loopend = location->end();
+	set_dirty ();
 }
 
 void