diff --git a/libs/ardour/ardour/event_type_map.h b/libs/ardour/ardour/event_type_map.h
index d6f26aeac7..b0ccdc8efd 100644
--- a/libs/ardour/ardour/event_type_map.h
+++ b/libs/ardour/ardour/event_type_map.h
@@ -24,7 +24,7 @@
 #include <string>
 #include <evoral/TypeMap.hpp>
 
-class Evoral::Parameter;
+namespace Evoral { class Parameter; }
 
 namespace ARDOUR {