diff --git a/libs/ardour/midi_source.cc b/libs/ardour/midi_source.cc
index f7be87cb75..2f0affb64f 100644
--- a/libs/ardour/midi_source.cc
+++ b/libs/ardour/midi_source.cc
@@ -23,7 +23,9 @@
  */
 
 #include <sys/stat.h>
+#ifdef HAVE_UNISTD_H
 #include <unistd.h>
+#endif
 #include <fcntl.h>
 #include <float.h>
 #include <cerrno>