diff --git a/libs/ardour/ardour/triggerbox.h b/libs/ardour/ardour/triggerbox.h
index 998a1b282b..3adee3de7b 100644
--- a/libs/ardour/ardour/triggerbox.h
+++ b/libs/ardour/ardour/triggerbox.h
@@ -729,6 +729,8 @@ class LIBARDOUR_API TriggerBox : public Processor
 	XMLNode& get_state () const;
 	int set_state (const XMLNode&, int version);
 
+	void deep_sources (std::set<boost::shared_ptr<Source>>&);
+
 	void set_from_path (uint32_t slot, std::string const & path);
 	void set_from_selection (uint32_t slot, boost::shared_ptr<Region>);
 
diff --git a/libs/ardour/session_state.cc b/libs/ardour/session_state.cc
index 9f55e21ca6..552310b0e2 100644
--- a/libs/ardour/session_state.cc
+++ b/libs/ardour/session_state.cc
@@ -3667,8 +3667,17 @@ Session::cleanup_sources (CleanupReport& rep)
 
 	_playlists->foreach (boost::bind (merge_all_sources, _1, &sources_used_by_this_snapshot));
 
-	/*  add our current source list
-	*/
+	{
+		boost::shared_ptr<RouteList> rl = routes.reader();
+		for (auto const& r : *rl) {
+			boost::shared_ptr<TriggerBox> tb = r->triggerbox ();
+			if (tb) {
+				tb->deep_sources (sources_used_by_this_snapshot);
+			}
+		}
+	}
+
+	/*  add our current source list */
 
 	ls.acquire ();
 	for (SourceMap::iterator i = sources.begin(); i != sources.end(); ) {
diff --git a/libs/ardour/triggerbox.cc b/libs/ardour/triggerbox.cc
index a5de1a359c..0f48378d30 100644
--- a/libs/ardour/triggerbox.cc
+++ b/libs/ardour/triggerbox.cc
@@ -3250,6 +3250,17 @@ TriggerBox::trigger_by_id (PBD::ID check)
 	return TriggerPtr();
 }
 
+void
+TriggerBox::deep_sources (std::set<boost::shared_ptr<Source> >& sources)
+{
+	for (uint64_t n = 0; n < all_triggers.size(); ++n) {
+		boost::shared_ptr<Region> r (trigger(n)->region ());
+		if (r) {
+			r->deep_sources (sources);
+		}
+	}
+}
+
 void
 TriggerBox::enqueue_trigger_state_for_region (boost::shared_ptr<Region> region, boost::shared_ptr<Trigger::UIState> state)
 {