diff --git a/libs/ardour/session.cc b/libs/ardour/session.cc
index 604e704cd1..6bfe155edc 100644
--- a/libs/ardour/session.cc
+++ b/libs/ardour/session.cc
@@ -3681,6 +3681,8 @@ Session::add_routes_inner (RouteList& new_routes, bool input_auto_connect, bool
 					r->enable_direct_outs ();
 				}
 			}
+			/* do not take `_auto_connect_queue_lock' while holding the process lock */
+			lm.release ();
 			reassign_track_numbers ();
 		}
 	}