diff --git a/libs/ardour/luabindings.cc b/libs/ardour/luabindings.cc
index 2157763d7c..a642d92864 100644
--- a/libs/ardour/luabindings.cc
+++ b/libs/ardour/luabindings.cc
@@ -297,6 +297,7 @@ namespace LuaCairo {
 namespace LuaDialog {
 	class Message;
 	class Dialog;
+	class ProgressWindow;
 }
 
 namespace Cairo {