diff --git a/lib/libutil/pty.c b/lib/libutil/pty.c
index c60d250f443f..7e0640804082 100644
--- a/lib/libutil/pty.c
+++ b/lib/libutil/pty.c
@@ -47,6 +47,7 @@ static char sccsid[] = "@(#)pty.c	8.3 (Berkeley) 5/16/94";
 #include <stdlib.h>
 #include <string.h>
 #include <termios.h>
+#include <unistd.h>
 
 int
 openpty(int *amaster, int *aslave, char *name, struct termios *termp,