diff --git a/libs/ardour/ardour/surround_return.h b/libs/ardour/ardour/surround_return.h
index 4c6ad722e3..2f6eb70275 100644
--- a/libs/ardour/ardour/surround_return.h
+++ b/libs/ardour/ardour/surround_return.h
@@ -63,6 +63,14 @@ public:
 	void setup_export (std::string const&, samplepos_t, samplepos_t);
 	void finalize_export ();
 
+	size_t n_channels () const {
+		return _current_n_channels;
+	}
+
+	size_t total_n_channels () const {
+		return _total_n_channels;
+	}
+
 	std::shared_ptr<LV2Plugin> surround_processor () const {
 		return _surround_processor;
 	}
@@ -169,6 +177,7 @@ private:
 	int              _current_render_mode[max_object_id];
 	size_t           _channel_id_map[max_object_id];
 	size_t           _current_n_channels;
+	size_t           _total_n_channels;
 	MainOutputFormat _current_output_format;
 	BufferSet        _surround_bufs;
 	ChanMapping      _in_map;
diff --git a/libs/ardour/luabindings.cc b/libs/ardour/luabindings.cc
index 21d3e499ac..2a2ca18624 100644
--- a/libs/ardour/luabindings.cc
+++ b/libs/ardour/luabindings.cc
@@ -1927,6 +1927,8 @@ LuaBindings::common (lua_State* L)
 		.addFunction ("max_momentary", &SurroundReturn::max_momentary)
 		.addFunction ("momentary", &SurroundReturn::momentary)
 		.addFunction ("max_dbtp", &SurroundReturn::max_dbtp)
+		.addFunction ("n_channels", &SurroundReturn::n_channels)
+		.addFunction ("total_n_channels", &SurroundReturn::total_n_channels)
 		.addFunction ("output_format_controllable", &SurroundReturn::output_format_controllable)
 		.endClass ()
 
diff --git a/libs/ardour/surround_return.cc b/libs/ardour/surround_return.cc
index ed8ddfe271..1c5129daf5 100644
--- a/libs/ardour/surround_return.cc
+++ b/libs/ardour/surround_return.cc
@@ -82,6 +82,7 @@ SurroundReturn::SurroundReturn (Session& s, Route* r)
 #endif
 	, _have_au_renderer (false)
 	, _current_n_channels (max_object_id)
+	, _total_n_channels (max_object_id)
 	, _current_output_format (OUTPUT_FORMAT_7_1_4)
 	, _in_map (ChanCount (DataType::AUDIO, 128))
 	, _out_map (ChanCount (DataType::AUDIO, 14 + 6 /* Loudness Meter */))
@@ -397,7 +398,12 @@ SurroundReturn::run (BufferSet& bufs, samplepos_t start_sample, samplepos_t end_
 		timepos_t unused_start, unused_end;
 		samplecnt_t latency = effective_latency ();
 
-		for (uint32_t s = 0; s < ss->bufs ().count ().n_audio () && cid < max_object_id; ++s, ++cid) {
+		for (uint32_t s = 0; s < ss->bufs ().count ().n_audio (); ++s, ++cid) {
+
+			if (cid >= max_object_id) {
+				continue;
+			}
+
 			std::shared_ptr<SurroundPannable> const& p (ss->pan_param (s, unused_start, unused_end));
 
 			AutoState const as        = p->automation_state ();
@@ -470,14 +476,12 @@ SurroundReturn::run (BufferSet& bufs, samplepos_t start_sample, samplepos_t end_
 #endif
 				}
 			}
-
-		}
-
-		if (cid >= max_object_id) {
-			break;
 		}
 	}
 
+	_total_n_channels = cid;
+	cid = std::min<size_t> (128, cid);
+
 	if (_current_n_channels != cid) {
 		_current_n_channels = cid;
 #if defined(LV2_EXTENDED) && defined(HAVE_LV2_1_10_0)