--- a/qmail-pw2u.c
+++ b/qmail-pw2u.c
@@ -1,3 +1,4 @@
+#include <unistd.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include "substdio.h"
--- a/qmail-qmtpd.c
+++ b/qmail-qmtpd.c
@@ -1,3 +1,4 @@
+#include <unistd.h>
 #include "stralloc.h"
 #include "substdio.h"
 #include "qmail.h"
--- a/readwrite.h
+++ b/readwrite.h
@@ -1,7 +1,7 @@
 #ifndef READWRITE_H
 #define READWRITE_H
 
-extern int read();
-extern int write();
+#include <fcntl.h>
+#include <unistd.h>
 
 #endif
--- a/substdio.h
+++ b/substdio.h
@@ -1,6 +1,8 @@
 #ifndef SUBSTDIO_H
 #define SUBSTDIO_H
 
+#include <unistd.h>
+
 typedef struct substdio {
   char *x;
   int p;