diff --git a/gtk2_ardour/au_pluginui.mm b/gtk2_ardour/au_pluginui.mm
index 76d29a5ce4..995678a752 100644
--- a/gtk2_ardour/au_pluginui.mm
+++ b/gtk2_ardour/au_pluginui.mm
@@ -29,6 +29,7 @@
 #include "pbd/convert.h"
 #include "pbd/error.h"
 
+#include "ardour/auditioner.h"
 #include "ardour/audio_unit.h"
 #include "ardour/debug.h"
 #include "ardour/plugin_insert.h"