diff --git a/CMakeLists.txt b/CMakeLists.txt
index df2a793..13686db 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -5,7 +5,6 @@ cmake_minimum_required(VERSION 3.22)
 project(eb VERSION 1.0.0 LANGUAGES C)
 
 set(SOURCES
-    custom_unistd.h
     appendix.c
     appendix.h
     appsub.c
diff --git a/build-post.h b/build-post.h
index 3f57722..6d6f5e3 100644
--- a/build-post.h
+++ b/build-post.h
@@ -33,8 +33,8 @@ extern "C" {
 #endif
 #include "defs.h"
 
-#if defined( __APPLE__) || defined(__linux__)
-  #include <dirent.h>
+#ifndef _WIN32
+#include <dirent.h>
 #else
   #include "win_dirent.h"
 #endif
diff --git a/build-pre.h b/build-pre.h
index 90d3fc6..07f2e50 100644
--- a/build-pre.h
+++ b/build-pre.h
@@ -40,7 +40,16 @@
 #include <stdlib.h>
 #include <stdarg.h>
 #include <limits.h>
-#include "custom_unistd.h"
+/*
+ * Platform abstraction for unistd.h.
+ * unistd.h maps (roughly) to io.h on Windows.
+ */
+#if defined(_WIN32)
+#include <io.h>
+#include <process.h>
+#else
+#include <unistd.h>
+#endif
 #include <fcntl.h>
 
 #if defined( _WIN32 )
diff --git a/custom_unistd.h b/custom_unistd.h
deleted file mode 100644
index 221988d..0000000
--- a/custom_unistd.h
+++ /dev/null
@@ -1,14 +0,0 @@
-/** This file is part of the Mingw32 package.
-
-unistd.h maps (roughly) to io.h
-*/
-#ifndef CUSTOM_UNISTD_H
-#define CUSTOM_UNISTD_H
-
-#if defined( __APPLE__) || defined(__linux__)
-#include <unistd.h>
-#else
-#include <io.h>
-#include <process.h>
-#endif
-#endif /* _UNISTD_H */
diff --git a/filename.c b/filename.c
index 62ca2f3..89960e3 100644
--- a/filename.c
+++ b/filename.c
@@ -32,11 +32,10 @@
 
 #include "build-post.h"
 
-
-#if defined( __APPLE__) || defined(__linux__)
-#include <dirent.h>
-#else
+#ifdef _WIN32
 #include "win_dirent.h"
+#else
+#include <dirent.h>
 #endif
 
 
diff --git a/zio.c b/zio.c
index e4621ae..a52fda0 100644
--- a/zio.c
+++ b/zio.c
@@ -27,7 +27,6 @@
  */
 
 #include "build-pre.h"
-#include "custom_unistd.h"
 #include <errno.h>
 #include <fcntl.h>
 #include <limits.h>