diff --git a/libs/ardour/ardour/port_insert.h b/libs/ardour/ardour/port_insert.h
index 72f02ff9c7..55f91569d5 100644
--- a/libs/ardour/ardour/port_insert.h
+++ b/libs/ardour/ardour/port_insert.h
@@ -58,7 +58,7 @@ class PortInsert : public IOProcessor
 	ChanCount output_streams() const;
 	ChanCount input_streams() const;
 
-	bool can_support_io_configuration (const ChanCount& in, ChanCount& out) const { return true; }
+	bool can_support_io_configuration (const ChanCount& in, ChanCount& out) const;
 	bool configure_io (ChanCount in, ChanCount out);
 
 	uint32_t bit_slot() const { return bitslot; }
diff --git a/libs/ardour/port_insert.cc b/libs/ardour/port_insert.cc
index 8c33d989dd..2e7f20ba66 100644
--- a/libs/ardour/port_insert.cc
+++ b/libs/ardour/port_insert.cc
@@ -212,3 +212,9 @@ PortInsert::input_streams() const
 	return _io->n_outputs ();
 }
 
+bool
+PortInsert::can_support_io_configuration (const ChanCount& in, ChanCount& out) const
+{
+	out = in;
+	return true;
+}
diff --git a/libs/ardour/route.cc b/libs/ardour/route.cc
index 14a8537068..452d611d87 100644
--- a/libs/ardour/route.cc
+++ b/libs/ardour/route.cc
@@ -1602,7 +1602,7 @@ Route::_reset_processor_counts (ProcessorStreams* err)
 			plugin_insert->set_count (1);
 
 		} else if ((port_insert = boost::dynamic_pointer_cast<PortInsert>(*r)) != 0) {
-			
+
 			++insert_cnt;
 			proc_map[(*r)->placement()].push_back (ProcessorCount (*r));
 
@@ -1635,7 +1635,7 @@ Route::_reset_processor_counts (ProcessorStreams* err)
 	if (!proc_map[PreFader].empty()) {
 		previous_initial_streams = n_inputs ();
 		for (list<ProcessorCount>::iterator i = proc_map[PreFader].begin(); i != proc_map[PreFader].end(); i++) {
-			if (i->processor->can_support_io_configuration (previous_initial_streams, initial_streams) < 0) {
+			if (i->processor->can_support_io_configuration (previous_initial_streams, initial_streams) == false) {
 				goto streamcount;
 			}
 			previous_initial_streams = initial_streams;
@@ -1650,7 +1650,7 @@ Route::_reset_processor_counts (ProcessorStreams* err)
 
 	if (!proc_map[PostFader].empty()) {
 		for (list<ProcessorCount>::iterator i = proc_map[PostFader].begin(); i != proc_map[PostFader].end(); i++) {
-			if (i->processor->can_support_io_configuration (previous_initial_streams, initial_streams) < 0) {
+			if (i->processor->can_support_io_configuration (previous_initial_streams, initial_streams) == false) {
 				goto streamcount;
 			}
 			previous_initial_streams = initial_streams;