diff --git a/Tools/unix/zx/config.h.darwin b/Tools/unix/zx/config.h.darwin
index d3a4bdb0..cc4b425c 100644
--- a/Tools/unix/zx/config.h.darwin
+++ b/Tools/unix/zx/config.h.darwin
@@ -2,10 +2,11 @@
 #define HAVE_DIRENT_H
 #define HAVE_UTIME_H
 #define HAVE_FCNTL_H
+#define	HAVE_UNISTD_H
 #define BINDIR80 getenv("ZXBINDIR")
 #define LIBDIR80 getenv("ZXLIBDIR")
 #define INCDIR80 getenv("ZXINCDIR")
-#define LINUX
+#define DARWIN
 #include <sys/param.h>
 #include <sys/mount.h>
 #define	_S_IFDIR S_IFDIR
diff --git a/Tools/unix/zx/config.h.linux b/Tools/unix/zx/config.h.linux
index bca1a709..a015591c 100644
--- a/Tools/unix/zx/config.h.linux
+++ b/Tools/unix/zx/config.h.linux
@@ -3,6 +3,7 @@
 #define HAVE_UTIME_H
 #define HAVE_FCNTL_H
 #define HAVE_SYS_VFS_H
+#define	HAVE_UNISTD_H
 #define BINDIR80 getenv("ZXBINDIR")
 #define LIBDIR80 getenv("ZXLIBDIR")
 #define INCDIR80 getenv("ZXINCDIR")
diff --git a/Tools/unix/zx/zx.h b/Tools/unix/zx/zx.h
index c2fd0930..dac69ce0 100644
--- a/Tools/unix/zx/zx.h
+++ b/Tools/unix/zx/zx.h
@@ -31,7 +31,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
-#ifdef LINUX
+#if defined(LINUX) || defined(DARWIN)
 #include <unistd.h>
 #define	_isatty(a) isatty(a)
 #define	_fileno(a) fileno(a)
@@ -87,7 +87,7 @@ extern char **argv;
 extern int argc;
 extern byte RAM[65536]; /* The Z80's address space */
 
-extern usestdio;
+extern int usestdio;
 
 /* Z80 CPU emulation */