diff --git a/gtk2_ardour/midi_tracer.cc b/gtk2_ardour/midi_tracer.cc
index 1fc50c103f..e447c59f3b 100644
--- a/gtk2_ardour/midi_tracer.cc
+++ b/gtk2_ardour/midi_tracer.cc
@@ -24,6 +24,7 @@
 #include <time.h>
 
 #include "pbd/localtime_r.h"
+#include "pbd/timersub.h"
 
 #include "midi++/parser.h"
 #include "midi++/manager.h"