diff --git a/libs/ardour/route.cc b/libs/ardour/route.cc
index 9660e78358..56cd04d84a 100644
--- a/libs/ardour/route.cc
+++ b/libs/ardour/route.cc
@@ -1636,8 +1636,9 @@ Route::try_configure_processors_unlocked (ChanCount in, ProcessorStreams* err)
 				 * Delivery::configure_io() will do the actual removal
 				 * by calling _output->ensure_io()
 				 */
-				if (!is_master() && _session.master_out ()) {
-					/* ..but at least as many as there are master-inputs */
+				if (!is_master() && _session.master_out () && in.n_audio() > 0) {
+					/* ..but at least as many as there are master-inputs, if
+					 * the delivery is dealing with audio */
 					// XXX this may need special-casing for mixbus (master-outputs)
 					// and should maybe be a preference anyway ?!
 					out = ChanCount::max (in, _session.master_out ()->n_inputs ());