diff --git a/libs/ardour/audio_backend.cc b/libs/ardour/audio_backend.cc
index 286ecf78ca..1f485891d6 100644
--- a/libs/ardour/audio_backend.cc
+++ b/libs/ardour/audio_backend.cc
@@ -116,9 +116,6 @@ AudioBackend::setup_channel_masks (size_t in, size_t out)
 {
 	_input_channel_mask.assign (in, true);
 	_output_channel_mask.assign (out, true);
-
-	_input_channel_mask[2] = false;
-	_output_channel_mask[3] = false;
 }
 
 } // namespace ARDOUR