diff --git a/libs/ardour/ardour/triggerbox.h b/libs/ardour/ardour/triggerbox.h
index 0c119fd251..43975b73e2 100644
--- a/libs/ardour/ardour/triggerbox.h
+++ b/libs/ardour/ardour/triggerbox.h
@@ -730,6 +730,7 @@ class LIBARDOUR_API TriggerBox : public Processor
 	int set_state (const XMLNode&, int version);
 
 	void deep_sources (std::set<boost::shared_ptr<Source>>&);
+	void used_regions (std::set<boost::shared_ptr<Region>>&);
 
 	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 99adb50162..4c3b8d8785 100644
--- a/libs/ardour/session_state.cc
+++ b/libs/ardour/session_state.cc
@@ -3500,10 +3500,26 @@ Session::cleanup_regions ()
 	bool removed = false;
 	const RegionFactory::RegionMap& regions (RegionFactory::regions());
 
+	/* collect Regions used by Triggers */
+	std::set<boost::shared_ptr<Region>> tr;
+	{
+		boost::shared_ptr<RouteList> rl = routes.reader();
+		for (auto const& r : *rl) {
+			boost::shared_ptr<TriggerBox> tb = r->triggerbox ();
+			if (tb) {
+				tb->used_regions (tr);
+			}
+		}
+	}
+
 	for (RegionFactory::RegionMap::const_iterator i = regions.begin(); i != regions.end();) {
 
 		uint32_t used = _playlists->region_use_count (i->second);
 
+		if (tr.find (i->second) != tr.end()) {
+			++used;
+		}
+
 		if (used == 0 && !i->second->automatic ()) {
 			boost::weak_ptr<Region> w = i->second;
 			++i;
diff --git a/libs/ardour/triggerbox.cc b/libs/ardour/triggerbox.cc
index ba4755f82f..302cfb7cb6 100644
--- a/libs/ardour/triggerbox.cc
+++ b/libs/ardour/triggerbox.cc
@@ -3340,6 +3340,8 @@ TriggerBox::trigger_by_id (PBD::ID check)
 void
 TriggerBox::deep_sources (std::set<boost::shared_ptr<Source> >& sources)
 {
+	Glib::Threads::RWLock::ReaderLock lm (trigger_lock);
+
 	for (uint64_t n = 0; n < all_triggers.size(); ++n) {
 		boost::shared_ptr<Region> r (trigger(n)->region ());
 		if (r) {
@@ -3348,6 +3350,20 @@ TriggerBox::deep_sources (std::set<boost::shared_ptr<Source> >& sources)
 	}
 }
 
+void
+TriggerBox::used_regions (std::set<boost::shared_ptr<Region> >& regions)
+{
+	Glib::Threads::RWLock::ReaderLock lm (trigger_lock);
+
+	for (uint64_t n = 0; n < all_triggers.size(); ++n) {
+		boost::shared_ptr<Region> r (trigger(n)->region ());
+		if (r) {
+			regions.insert (r);
+		}
+	}
+}
+
+
 void
 TriggerBox::enqueue_trigger_state_for_region (boost::shared_ptr<Region> region, boost::shared_ptr<Trigger::UIState> state)
 {