diff --git a/code/os/win/io.c b/code/os/win/io.c
new file mode 100644
index 0000000..795659a
--- /dev/null
+++ b/code/os/win/io.c
@@ -0,0 +1,15 @@
+
+#define WIN32_LEAN_AND_MEAN
+#include <Windows.h>
+
+// It's just mapped directly to HANDLE
+struct FILE {
+    int unused;
+};
+
+void _file_write(void* ctx, size_t n, const char str[]) {
+    DWORD written = 0;
+    WriteFile((HANDLE) ctx, str, n, &written, NULL);
+}
+
+
diff --git a/code/stdio.c b/code/stdio.c
index 1db2ec8..4ffde74 100644
--- a/code/stdio.c
+++ b/code/stdio.c
@@ -7,6 +7,8 @@
 #define __STDC_WANT_LIB_EXT1__ 1
 #include <string.h>
 
+#include <_os.h>
+
 typedef void(*OutputFunc)(void* ctx, size_t n, const char str[]);
 
 ///////////////////////////////////////////////
@@ -18,29 +20,6 @@ typedef void(*OutputFunc)(void* ctx, size_t n, const char str[]);
 #define FMT_STRLEN_S(s, maxsize) strnlen_s(s, maxsize)
 #include "printf.h"
 
-///////////////////////////////////////////////
-// Platform dependent
-///////////////////////////////////////////////
-#if defined(_os_win)
-#define WIN32_LEAN_AND_MEAN
-#include <Windows.h>
-
-// It's just mapped directly to HANDLE
-struct FILE {
-    int unused;
-};
-
-static void file_write(void* ctx, size_t n, const char str[]) {
-    DWORD written = 0;
-    WriteFile((HANDLE) ctx, str, n, &written, NULL);
-}
-#else
-#error "TODO: Implement this"
-#endif
-
-///////////////////////////////////////////////
-// Platform indenpendent
-///////////////////////////////////////////////
 typedef struct {
     size_t used, capacity;
     char* string;
@@ -61,12 +40,12 @@ static void string_write(void *ctx, size_t n, const char *restrict str) {
 }
 
 int fprintf(FILE *file, const char *restrict fmt, ...) {
-	CALL_PRINTF(fmt_print_char, file, file_write, fmt);
+	CALL_PRINTF(fmt_print_char, file, _file_write, fmt);
 	return result;
 }
 
 int printf(const char *restrict fmt, ...) {
-    CALL_PRINTF(fmt_print_char, stdout, file_write, fmt);
+    CALL_PRINTF(fmt_print_char, stdout, _file_write, fmt);
 	return result;
 }
 
@@ -83,11 +62,11 @@ int sprintf(char *restrict s, const char *restrict fmt, ...) {
 }
 
 int vfprintf(FILE *file, const char *restrict fmt, va_list args) {
-	return fmt_print_char(file, file_write, fmt, args);
+	return fmt_print_char(file, _file_write, fmt, args);
 }
 
 int vprintf(const char *restrict fmt, va_list args) {
-	return fmt_print_char(stdout, file_write, fmt, args);
+	return fmt_print_char(stdout, _file_write, fmt, args);
 }
 
 int vsnprintf(char *restrict s, size_t n, const char *restrict fmt, va_list args) {
diff --git a/inc/_os.h b/inc/_os.h
index cc49a99..253bdc6 100644
--- a/inc/_os.h
+++ b/inc/_os.h
@@ -13,3 +13,7 @@
    || defined(_os_linux))
     #error "Unsupported OS"
 #endif
+
+// OS-dependent IO Functions
+void _file_write(void* ctx, size_t n, const char str[]);
+typedef struct FILE FILE;
diff --git a/inc/stdio.h b/inc/stdio.h
index b2f59a9..e867634 100644
--- a/inc/stdio.h
+++ b/inc/stdio.h
@@ -6,6 +6,10 @@
 typedef struct FILE FILE;
 typedef int64_t fpos_t;
 
+#if !defined(NULL)
+    #define NULL ((void *)0)
+#endif
+
 #if !defined(__STDC_LIB_EXT1__)
     #define __STDC_LIB_EXT1__
     typedef int errno_t;
@@ -29,9 +33,9 @@ typedef int64_t fpos_t;
 #define FOPEN_MAX 20
 
 #ifdef _os_win
-#define FILENAME_MAX 260
+    #define FILENAME_MAX 260
 #else
-#define FILENAME_MAX 4096
+    #define FILENAME_MAX 4096
 #endif
 
 #define L_tmpnam FILENAME_MAX
@@ -40,7 +44,11 @@ typedef int64_t fpos_t;
 #define SEEK_END 2
 #define SEEK_SET 0
 
-#define TMP_MAX  INT_MAX
+#ifdef _os_win
+    #define TMP_MAX  SHORT_MAX
+#else
+    #define TMP_MAX INT_MAX
+#endif
 
 extern FILE *stdout, *stderr, *stdin;