diff --git a/libs/ardour/session_midi.cc b/libs/ardour/session_midi.cc
index 0f13d47d2f..02dc1c1c43 100644
--- a/libs/ardour/session_midi.cc
+++ b/libs/ardour/session_midi.cc
@@ -29,7 +29,9 @@
 #include <memory>
 #include <string>
 
+#ifdef HAVE_UNISTD_H
 #include <unistd.h>
+#endif
 
 #include <glibmm/main.h>