diff --git a/libs/ardour/butler.cc b/libs/ardour/butler.cc
index c9e52cb42c..afb33f6bf7 100644
--- a/libs/ardour/butler.cc
+++ b/libs/ardour/butler.cc
@@ -22,7 +22,9 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#ifdef HAVE_UNISTD_H
 #include <unistd.h>
+#endif
 
 #ifdef HAVE_IOPRIO
 #include <sys/syscall.h>