diff --git a/libs/ardour/ardour/plugin_insert.h b/libs/ardour/ardour/plugin_insert.h
index 2ba4c10b02..3893cbc57a 100644
--- a/libs/ardour/ardour/plugin_insert.h
+++ b/libs/ardour/ardour/plugin_insert.h
@@ -135,6 +135,7 @@ public:
 	void set_output_map (uint32_t, ChanMapping);
 	void set_thru_map (ChanMapping);
 	bool reset_map (bool emit = true);
+	bool reset_sidechain_map ();
 	bool configured () const { return _configured; }
 
 	// these are ports visible on the outside
diff --git a/libs/ardour/plugin_insert.cc b/libs/ardour/plugin_insert.cc
index 786f283e96..8d27e8704e 100644
--- a/libs/ardour/plugin_insert.cc
+++ b/libs/ardour/plugin_insert.cc
@@ -1968,6 +1968,53 @@ PluginInsert::reset_map (bool emit)
 	return true;
 }
 
+bool
+PluginInsert::reset_sidechain_map ()
+{
+	/* intended to be called from Route::add_remove_sidechain after
+	 * adding a SC. This connects the SC ports like reset_map() above.
+	 */
+
+	if (!has_sidechain () || sidechain_input_pins ().n_total () == 0) {
+		return false;
+	}
+	if (_custom_cfg) {
+		return false;
+	}
+
+	const PinMappings old_in (_in_map);
+	for (DataType::iterator t = DataType::begin(); t != DataType::end(); ++t) {
+		uint32_t sc = 0; // side-chain round-robin (all instances)
+		uint32_t pc = 0;
+		for (Plugins::iterator i = _plugins.begin(); i != _plugins.end(); ++i, ++pc) {
+			const uint32_t nis = natural_input_streams ().get(*t);
+
+			/* SC inputs are last in the plugin-insert.. */
+			const uint32_t sc_start = _configured_in.get (*t);
+			const uint32_t sc_len = _configured_internal.get (*t) - sc_start;
+
+			for (uint32_t in = 0; in < nis; ++in) {
+				const Plugin::IOPortDescription& iod (_plugins[pc]->describe_io_port (*t, true, in));
+				if (iod.is_sidechain) {
+					/* connect sidechain sinks to sidechain inputs in round-robin fashion */
+					if (sc_len > 0) {// side-chain may be hidden
+						_in_map[pc].set (*t, in, sc_start + sc);
+						sc = (sc + 1) % sc_len;
+					}
+				}
+			}
+		}
+	}
+
+	sanitize_maps ();
+	if (old_in == _in_map) {
+		return false;
+	}
+
+	mapping_changed ();
+	return true;
+}
+
 bool
 PluginInsert::configure_io (ChanCount in, ChanCount out)
 {
diff --git a/libs/ardour/route.cc b/libs/ardour/route.cc
index 09d20e4612..5e14f6dd54 100644
--- a/libs/ardour/route.cc
+++ b/libs/ardour/route.cc
@@ -2353,7 +2353,11 @@ Route::add_remove_sidechain (boost::shared_ptr<Processor> proc, bool add)
 		PBD::Unwinder<bool> uw (_in_sidechain_setup, true);
 
 		if (add) {
-			if (!pi->add_sidechain ()) {
+			ChanCount sc (pi->sidechain_input_pins ());
+			if (sc.n_audio () == 0 && sc.n_midi () == 0) {
+				sc.set (DataType::AUDIO, 1);
+			}
+			if (!pi->add_sidechain (sc.n_audio (), sc.n_midi ())) {
 				return false;
 			}
 		} else {
@@ -2384,6 +2388,7 @@ Route::add_remove_sidechain (boost::shared_ptr<Processor> proc, bool add)
 	}
 
 	if (pi->has_sidechain ()) {
+		pi->reset_sidechain_map ();
 		pi->sidechain_input ()->changed.connect_same_thread (*pi, boost::bind (&Route::sidechain_change_handler, this, _1, _2));
 	}