diff --git a/libs/ardour/SConscript b/libs/ardour/SConscript
index e8e23f6a51..52943dd8fd 100644
--- a/libs/ardour/SConscript
+++ b/libs/ardour/SConscript
@@ -98,6 +98,8 @@ globals.cc
 import.cc
 io.cc
 io_processor.cc
+internal_send.cc
+internal_return.cc
 interpolation.cc
 jack_slave.cc
 ladspa_plugin.cc