diff --git a/libs/ardour/luabindings.cc b/libs/ardour/luabindings.cc
index 2c2c595d9c..2157763d7c 100644
--- a/libs/ardour/luabindings.cc
+++ b/libs/ardour/luabindings.cc
@@ -309,6 +309,7 @@ CLASSKEYS(LuaCairo::PangoLayout);
 
 CLASSKEYS(LuaDialog::Message);
 CLASSKEYS(LuaDialog::Dialog);
+CLASSKEYS(LuaDialog::ProgressWindow);
 
 #endif // end windows special case