diff --git a/libs/ardour/ardour/vst3_plugin.h b/libs/ardour/ardour/vst3_plugin.h
index 3cad78d02d..4e270ba03c 100644
--- a/libs/ardour/ardour/vst3_plugin.h
+++ b/libs/ardour/ardour/vst3_plugin.h
@@ -332,6 +332,9 @@ private:
 	int _n_midi_inputs;
 	int _n_midi_outputs;
 	int _n_factory_presets;
+
+	/* work around UADx plugin crash */
+	bool _no_kMono;
 };
 
 } // namespace Steinberg
diff --git a/libs/ardour/vst3_plugin.cc b/libs/ardour/vst3_plugin.cc
index 3dca859f9b..b28ffe4a76 100644
--- a/libs/ardour/vst3_plugin.cc
+++ b/libs/ardour/vst3_plugin.cc
@@ -1161,6 +1161,7 @@ VST3PI::VST3PI (std::shared_ptr<ARDOUR::VST3PluginModule> m, std::string unique_
 	, _owner (0)
 	, _add_to_selection (false)
 	, _n_factory_presets (0)
+	, _no_kMono (false)
 {
 	using namespace std;
 	IPluginFactory* factory = m->factory ();
@@ -1173,6 +1174,16 @@ VST3PI::VST3PI (std::shared_ptr<ARDOUR::VST3PluginModule> m, std::string unique_
 		throw failed_constructor ();
 	}
 
+	PFactoryInfo fi;
+	if (factory->getFactoryInfo (&fi) == kResultTrue) {
+		/* work around issue with UADx VST3s not recognizing
+		 * Vst::SpeakerArr::kMono. (see commit message for details)
+		 */
+		if (0 == strcmp (fi.vendor, "Universal Audio (UADx)")) {
+			_no_kMono = true;
+		}
+	}
+
 #ifndef NDEBUG
 	if (DEBUG_ENABLED (DEBUG::VST3Config)) {
 		char fuid[33];
@@ -2210,7 +2221,7 @@ VST3PI::enable_io (std::vector<bool> const& ins, std::vector<bool> const& outs)
 		}
 		cnt += n_chn;
 		/* special case for Left only == Mono */
-		if (sa == 1 /*Vst::SpeakerArr::kSpeakerL */) {
+		if (sa == 1 /*Vst::SpeakerArr::kSpeakerL */ && !_no_kMono) {
 			sa = Vst::SpeakerArr::kMono; /* 1 << 19 */
 		}
 
@@ -2234,7 +2245,7 @@ VST3PI::enable_io (std::vector<bool> const& ins, std::vector<bool> const& outs)
 		}
 		cnt += n_chn;
 		/* special case for Left only == Mono */
-		if (sa == 1 /*Vst::SpeakerArr::kSpeakerL */) {
+		if (sa == 1 /*Vst::SpeakerArr::kSpeakerL */ && !_no_kMono) {
 			sa = Vst::SpeakerArr::kMono; /* 1 << 19 */
 		}
 		DEBUG_TRACE (DEBUG::VST3Config, string_compose ("VST3PI::enable_io: activateBus (kAudio, kOutput, %1, %2) used-chn: %3 spk-arr: %4\n", sa_out.size (), enable, _bus_info_out[sa_out.size ()].n_used_chn, std::hex, sa));