diff --git a/libs/ardour/ardour/lv2_plugin.h b/libs/ardour/ardour/lv2_plugin.h
index 8f06b62b4c..ec59cc4f14 100644
--- a/libs/ardour/ardour/lv2_plugin.h
+++ b/libs/ardour/ardour/lv2_plugin.h
@@ -255,7 +255,8 @@ class LIBARDOUR_API LV2Plugin : public ARDOUR::Plugin, public ARDOUR::Workee
 		PORT_AUTOCTRL = 1 << 9,  ///< Event port supports auto:AutomationControl
 		PORT_CTRLED   = 1 << 10, ///< Port prop auto:AutomationControlled (can be self controlled)
 		PORT_CTRLER   = 1 << 11, ///< Port prop auto:AutomationController (can be self set)
-		PORT_NOAUTO   = 1 << 12  ///< Port don't allow to automate
+		PORT_NOAUTO   = 1 << 12, ///< Port don't allow to automate
+		PORT_OTHOPT   = 1 << 13  ///< Port of unknown data type with prop connectionOptional
 	} PortFlag;
 
 	typedef unsigned PortFlags;
diff --git a/libs/ardour/lv2_plugin.cc b/libs/ardour/lv2_plugin.cc
index c21229886a..1c9608e865 100644
--- a/libs/ardour/lv2_plugin.cc
+++ b/libs/ardour/lv2_plugin.cc
@@ -838,7 +838,9 @@ LV2Plugin::init(const void* c_plugin, samplecnt_t rate)
 			lilv_nodes_free(min_size_v);
 			lilv_nodes_free(buffer_types);
 			lilv_nodes_free(atom_supports);
-		} else if (!lilv_port_has_property(_impl->plugin, port, _world.lv2_connectionOptional)) {
+		} else if (lilv_port_has_property(_impl->plugin, port, _world.lv2_connectionOptional)) {
+			flags |= PORT_OTHOPT; // unknown data type but connection optional
+		} else {
 			error << string_compose(
 				"LV2: \"%1\" port %2 has no known data type",
 				lilv_node_as_string(_impl->name), i) << endmsg;
@@ -2994,6 +2996,8 @@ LV2Plugin::connect_and_run(BufferSet& bufs,
 			}
 
 			buf = lv2_evbuf_get_buffer(_ev_buffers[port_index]);
+		} else if(flags & PORT_OTHOPT) {
+			// Explicitely connect optional ports that we can not handle to NULL
 		} else {
 			continue;  // Control port, leave buffer alone
 		}
@@ -3453,6 +3457,8 @@ LV2Plugin::latency_compute_run()
 			ev_buffers.push_back (lv2_evbuf_new (buf_size, _uri_map.urids.atom_Chunk, _uri_map.urids.atom_Sequence));
 			void* buf = lv2_evbuf_get_buffer (ev_buffers.back ());
 			lilv_instance_connect_port(_impl->instance, port_index, buf);
+		} else if (flags & PORT_OTHOPT) {
+			lilv_instance_connect_port(_impl->instance, port_index, NULL);
 		}
 	}
 
@@ -3974,7 +3980,7 @@ LV2PluginInfo::discover (boost::function <void (std::string const&, PluginScanLo
 					count_ctrl_out++;
 				}
 			}
-			else if (!lilv_port_is_a(p, port, world.lv2_AudioPort) && !lilv_port_has_property(p, port, world.lv2_connectionOptional)) {
+			else if (!(lilv_port_is_a(p, port, world.lv2_AudioPort) || lilv_port_has_property(p, port, world.lv2_connectionOptional))) {
 				err = 1;
 				LilvNode* name = lilv_port_get_name(p, port);
 				cb (uri, PluginScanLogEntry::Error, string_compose (_("Port %1 ('%2') has no known data type"), i, lilv_node_as_string (name)), false);