diff --git a/libs/ardour/ardour/port_engine_shared.h b/libs/ardour/ardour/port_engine_shared.h
index 1ffe7a5e15..25ecd3c276 100644
--- a/libs/ardour/ardour/port_engine_shared.h
+++ b/libs/ardour/ardour/port_engine_shared.h
@@ -29,6 +29,7 @@
 
 #include "pbd/natsort.h"
 #include "pbd/rcu.h"
+#include "pbd/g_atomic_compat.h"
 
 #include "ardour/libardour_visibility.h"
 #include "ardour/port_engine.h"