diff --git a/libs/ardour/worker.cc b/libs/ardour/worker.cc
index d48ac959ba..b13398c69d 100644
--- a/libs/ardour/worker.cc
+++ b/libs/ardour/worker.cc
@@ -18,6 +18,7 @@
 */
 
 #include <stdlib.h>
+#include <unistd.h>
 
 #include "ardour/worker.h"
 #include "pbd/error.h"