diff --git a/libs/pbd/pbd/event_loop.h b/libs/pbd/pbd/event_loop.h
index 90d72ef47c..90184c7c06 100644
--- a/libs/pbd/pbd/event_loop.h
+++ b/libs/pbd/pbd/event_loop.h
@@ -25,6 +25,7 @@
 #include <map>
 #include <boost/function.hpp>
 #include <boost/bind.hpp> /* we don't need this here, but anything calling call_slot() probably will, so this is convenient */
+#include <pthread.h>
 #include <glibmm/threads.h>
 
 #include "pbd/libpbd_visibility.h"