diff --git a/libs/midi++2/jack_midi_port.cc b/libs/midi++2/jack_midi_port.cc
index e1a68b6475..57ca2b3629 100644
--- a/libs/midi++2/jack_midi_port.cc
+++ b/libs/midi++2/jack_midi_port.cc
@@ -19,6 +19,7 @@
 */
 #include <iostream>
 #include <cstdio>
+#include <unistd.h>
 #include <fcntl.h>
 #include <errno.h>