diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9e9b78c..0925fdc 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -45,7 +45,6 @@ if(WIN32)
   endif()
 
   target_sources(kabufuda PRIVATE
-    include/kabufuda/winsupport.hpp
     lib/kabufuda/AsyncIOWin32.cpp
   )
 elseif(NX)
diff --git a/include/kabufuda/AsyncIO.hpp b/include/kabufuda/AsyncIO.hpp
index def8334..242dcb3 100644
--- a/include/kabufuda/AsyncIO.hpp
+++ b/include/kabufuda/AsyncIO.hpp
@@ -9,8 +9,7 @@ using SizeReturn = ssize_t;
 using SizeReturn = ssize_t;
 #endif
 #else
-#include <windows.h>
-using SizeReturn = DWORD;
+using SizeReturn = unsigned long;
 #endif
 
 #include <cstddef>
@@ -19,6 +18,9 @@ using SizeReturn = DWORD;
 #include "kabufuda/Util.hpp"
 
 namespace kabufuda {
+#if _WIN32
+struct AsyncIOInner;
+#endif
 
 class AsyncIO {
 #ifdef __SWITCH__
@@ -27,11 +29,10 @@ class AsyncIO {
   int m_fd = -1;
   std::vector<std::pair<struct aiocb, SizeReturn>> m_queue;
 #else
-  HANDLE m_fh = INVALID_HANDLE_VALUE;
-  std::vector<std::pair<OVERLAPPED, SizeReturn>> m_queue;
+  AsyncIOInner* m_inner;
 #endif
   void _waitForOperation(size_t qIdx) const;
-  size_t m_maxBlock = 0;
+  mutable size_t m_maxBlock = 0;
 
 public:
   AsyncIO() = default;
@@ -41,11 +42,7 @@ public:
   AsyncIO& operator=(AsyncIO&& other);
   AsyncIO(const AsyncIO* other) = delete;
   AsyncIO& operator=(const AsyncIO& other) = delete;
-  void resizeQueue(size_t queueSz) {
-#ifndef __SWITCH__
-    m_queue.resize(queueSz);
-#endif
-  }
+  void resizeQueue(size_t queueSz);
   bool asyncRead(size_t qIdx, void* buf, size_t length, off_t offset);
   bool asyncWrite(size_t qIdx, const void* buf, size_t length, off_t offset);
   ECardResult pollStatus(size_t qIdx, SizeReturn* szRet = nullptr) const;
@@ -56,7 +53,7 @@ public:
 #elif !defined(_WIN32)
   explicit operator bool() const { return m_fd != -1; }
 #else
-  explicit operator bool() const { return m_fh != INVALID_HANDLE_VALUE; }
+  explicit operator bool() const;
 #endif
 };
 
diff --git a/include/kabufuda/Util.hpp b/include/kabufuda/Util.hpp
index 099225e..5144e7e 100644
--- a/include/kabufuda/Util.hpp
+++ b/include/kabufuda/Util.hpp
@@ -11,15 +11,6 @@
 #include <dirent.h>
 #include <fcntl.h>
 #include <unistd.h>
-#else
-#ifndef WIN32_LEAN_AND_MEAN
-#define WIN32_LEAN_AND_MEAN 1
-#endif
-#ifndef NOMINMAX
-#define NOMINMAX
-#endif
-#include <Windows.h>
-#include "winsupport.hpp"
 #endif
 
 #include <algorithm>
@@ -188,35 +179,10 @@ uint64_t getGCTime();
 #endif
 
 #if _WIN32
-class WStringConv {
-  std::wstring m_sys;
-
-public:
-  explicit WStringConv(std::string_view str) {
-    int len = MultiByteToWideChar(CP_UTF8, 0, str.data(), str.size(), nullptr, 0);
-    m_sys.assign(len, L'\0');
-    MultiByteToWideChar(CP_UTF8, 0, str.data(), str.size(), &m_sys[0], len);
-  }
-  [[nodiscard]] std::wstring str() const { return m_sys; }
-  [[nodiscard]] const wchar_t* c_str() const { return m_sys.c_str(); }
-};
-#endif
-
-inline int Stat(const char* path, Sstat* statOut) {
-#if _WIN32
-  size_t pos;
-  WStringConv wpath(path);
-  const wchar_t* wpathP = wpath.c_str();
-  for (pos = 0; pos < 3 && wpathP[pos] != L'\0'; ++pos) {}
-  if (pos == 2 && wpathP[1] == L':') {
-    wchar_t fixPath[4] = {wpathP[0], L':', L'/', L'\0'};
-    return _wstat64(fixPath, statOut);
-  }
-  return _wstat64(wpath.c_str(), statOut);
+int Stat(const char* path, Sstat* statOut);
 #else
-  return stat(path, statOut);
+inline int Stat(const char* path, Sstat* statOut) { return stat(path, statOut); }
 #endif
-}
 
 /**
  * @brief calculateChecksum
diff --git a/include/kabufuda/winsupport.hpp b/include/kabufuda/winsupport.hpp
deleted file mode 100644
index b66b9e9..0000000
--- a/include/kabufuda/winsupport.hpp
+++ /dev/null
@@ -1,34 +0,0 @@
-#pragma once
-
-#ifndef WIN32_LEAN_AND_MEAN
-#define WIN32_LEAN_AND_MEAN 1
-#endif
-#ifndef NOMINMAX
-#define NOMINMAX 1
-#endif
-#include "windows.h"
-#include <cstdint>
-
-#ifndef DEF_INLINE_MEMMEM
-#define DEF_INLINE_MEMMEM
-inline void* memmem(const void* haystack, size_t hlen, const void* needle, size_t nlen) {
-  int needle_first;
-  const uint8_t* p = static_cast<const uint8_t*>(haystack);
-  size_t plen = hlen;
-
-  if (!nlen)
-    return NULL;
-
-  needle_first = *(unsigned char*)needle;
-
-  while (plen >= nlen && (p = static_cast<const uint8_t*>(memchr(p, needle_first, plen - nlen + 1)))) {
-    if (!memcmp(p, needle, nlen))
-      return (void*)p;
-
-    p++;
-    plen = hlen - (p - static_cast<const uint8_t*>(haystack));
-  }
-
-  return NULL;
-}
-#endif
diff --git a/lib/kabufuda/AsyncIONX.cpp b/lib/kabufuda/AsyncIONX.cpp
index cf1e87c..5075115 100644
--- a/lib/kabufuda/AsyncIONX.cpp
+++ b/lib/kabufuda/AsyncIONX.cpp
@@ -45,4 +45,6 @@ ECardResult AsyncIO::pollStatus() const { return ECardResult::READY; }
 
 void AsyncIO::waitForCompletion() const {}
 
+void AsyncIO::resizeQueue(size_t queueSz) {}
+
 } // namespace kabufuda
diff --git a/lib/kabufuda/AsyncIOPosix.cpp b/lib/kabufuda/AsyncIOPosix.cpp
index d9c8ef0..e429108 100644
--- a/lib/kabufuda/AsyncIOPosix.cpp
+++ b/lib/kabufuda/AsyncIOPosix.cpp
@@ -142,4 +142,8 @@ void AsyncIO::waitForCompletion() const {
   const_cast<AsyncIO*>(this)->m_maxBlock = 0;
 }
 
+void AsyncIO::resizeQueue(size_t queueSz) {
+  m_queue.resize(queueSz);
+}
+
 } // namespace kabufuda
diff --git a/lib/kabufuda/AsyncIOWin32.cpp b/lib/kabufuda/AsyncIOWin32.cpp
index aeaa791..3e80be9 100644
--- a/lib/kabufuda/AsyncIOWin32.cpp
+++ b/lib/kabufuda/AsyncIOWin32.cpp
@@ -1,12 +1,47 @@
 #include "kabufuda/AsyncIO.hpp"
 
+#ifndef WIN32_LEAN_AND_MEAN
+#define WIN32_LEAN_AND_MEAN 1
+#endif
+#ifndef NOMINMAX
+#define NOMINMAX 1
+#endif
+#include <Windows.h>
+
 #include <algorithm>
 #include <cstdio>
 
 namespace kabufuda {
 
-#undef min
-#undef max
+class WStringConv {
+  std::wstring m_sys;
+
+public:
+  explicit WStringConv(std::string_view str) {
+    int len = MultiByteToWideChar(CP_UTF8, 0, str.data(), str.size(), nullptr, 0);
+    m_sys.assign(len, L'\0');
+    MultiByteToWideChar(CP_UTF8, 0, str.data(), str.size(), &m_sys[0], len);
+  }
+  [[nodiscard]] std::wstring str() const { return m_sys; }
+  [[nodiscard]] const wchar_t* c_str() const { return m_sys.c_str(); }
+};
+
+int Stat(const char* path, Sstat* statOut) {
+  size_t pos;
+  WStringConv wpath(path);
+  const wchar_t* wpathP = wpath.c_str();
+  for (pos = 0; pos < 3 && wpathP[pos] != L'\0'; ++pos) {}
+  if (pos == 2 && wpathP[1] == L':') {
+    wchar_t fixPath[4] = {wpathP[0], L':', L'/', L'\0'};
+    return _wstat64(fixPath, statOut);
+  }
+  return _wstat64(wpath.c_str(), statOut);
+}
+
+struct AsyncIOInner {
+  HANDLE m_fh = INVALID_HANDLE_VALUE;
+  std::vector<std::pair<OVERLAPPED, SizeReturn>> m_queue;
+};
 
 static void ResetOverlapped(OVERLAPPED& aio, DWORD offset = 0) {
   aio.Internal = 0;
@@ -15,60 +50,70 @@ static void ResetOverlapped(OVERLAPPED& aio, DWORD offset = 0) {
   aio.OffsetHigh = 0;
 }
 
-AsyncIO::AsyncIO(std::string_view filename, bool truncate) {
+AsyncIO::AsyncIO(std::string_view filename, bool truncate) : m_inner(new AsyncIOInner) {
 #if WINDOWS_STORE
   CREATEFILE2_EXTENDED_PARAMETERS parms = {};
   parms.dwSize = sizeof(CREATEFILE2_EXTENDED_PARAMETERS);
   parms.dwFileAttributes = FILE_ATTRIBUTE_NORMAL;
   parms.dwFileFlags = FILE_FLAG_OVERLAPPED;
-  m_fh = CreateFile2(filename.data(), GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE,
-                     truncate ? CREATE_ALWAYS : OPEN_ALWAYS, &parms);
+  m_inner->m_fh = CreateFile2(filename.data(), GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE,
+                              truncate ? CREATE_ALWAYS : OPEN_ALWAYS, &parms);
 #else
   WStringConv wfilename(filename);
-  m_fh = CreateFileW(wfilename.c_str(), GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, nullptr,
-                     truncate ? CREATE_ALWAYS : OPEN_ALWAYS, FILE_FLAG_OVERLAPPED | FILE_ATTRIBUTE_NORMAL, nullptr);
+  m_inner->m_fh =
+      CreateFileW(wfilename.c_str(), GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, nullptr,
+                  truncate ? CREATE_ALWAYS : OPEN_ALWAYS, FILE_FLAG_OVERLAPPED | FILE_ATTRIBUTE_NORMAL, nullptr);
 #endif
 }
 
 AsyncIO::~AsyncIO() {
   if (*this) {
-    if (CancelIoEx(m_fh, nullptr))
+    if (CancelIoEx(m_inner->m_fh, nullptr))
       waitForCompletion();
-    CloseHandle(m_fh);
+    CloseHandle(m_inner->m_fh);
   }
+  delete m_inner;
 }
 
 AsyncIO::AsyncIO(AsyncIO&& other) {
-  m_fh = other.m_fh;
-  other.m_fh = INVALID_HANDLE_VALUE;
-  m_queue = std::move(other.m_queue);
+  if (*this) {
+    if (CancelIoEx(m_inner->m_fh, nullptr))
+      waitForCompletion();
+    CloseHandle(m_inner->m_fh);
+  }
+  delete m_inner;
+  m_inner = other.m_inner;
+  other.m_inner = nullptr;
   m_maxBlock = other.m_maxBlock;
 }
 
 AsyncIO& AsyncIO::operator=(AsyncIO&& other) {
   if (*this) {
-    if (CancelIoEx(m_fh, nullptr))
+    if (CancelIoEx(m_inner->m_fh, nullptr))
       waitForCompletion();
-    CloseHandle(m_fh);
+    CloseHandle(m_inner->m_fh);
   }
-  m_fh = other.m_fh;
-  other.m_fh = INVALID_HANDLE_VALUE;
-  m_queue = std::move(other.m_queue);
+  delete m_inner;
+  m_inner = other.m_inner;
+  other.m_inner = nullptr;
   m_maxBlock = other.m_maxBlock;
   return *this;
 }
 
 void AsyncIO::_waitForOperation(size_t qIdx) const {
-  auto& aio = const_cast<AsyncIO*>(this)->m_queue[qIdx];
+  if (m_inner == nullptr) {
+    return;
+  }
+  auto& aio = m_inner->m_queue[qIdx];
   if (aio.first.hEvent == 0)
     return;
-  GetOverlappedResult(m_fh, &aio.first, &aio.second, TRUE);
+  GetOverlappedResult(m_inner->m_fh, &aio.first, &aio.second, TRUE);
   CloseHandle(aio.first.hEvent);
   aio.first.hEvent = 0;
 }
 
 bool AsyncIO::asyncRead(size_t qIdx, void* buf, size_t length, off_t offset) {
-  OVERLAPPED& aio = m_queue[qIdx].first;
+  OVERLAPPED& aio = m_inner->m_queue[qIdx].first;
   if (aio.hEvent) {
 #ifndef NDEBUG
     fprintf(stderr, "WARNING: synchronous kabufuda fallback, check access polling\n");
@@ -79,12 +124,12 @@ bool AsyncIO::asyncRead(size_t qIdx, void* buf, size_t length, off_t offset) {
   }
   ResetOverlapped(aio, DWORD(offset));
   m_maxBlock = std::max(m_maxBlock, qIdx + 1);
-  BOOL res = ReadFile(m_fh, buf, length, nullptr, &aio);
+  BOOL res = ReadFile(m_inner->m_fh, buf, length, nullptr, &aio);
   return res == TRUE || GetLastError() == ERROR_IO_PENDING;
 }
 
 bool AsyncIO::asyncWrite(size_t qIdx, const void* buf, size_t length, off_t offset) {
-  OVERLAPPED& aio = m_queue[qIdx].first;
+  OVERLAPPED& aio = m_inner->m_queue[qIdx].first;
   if (aio.hEvent) {
 #ifndef NDEBUG
     fprintf(stderr, "WARNING: synchronous kabufuda fallback, check access polling\n");
@@ -95,18 +140,18 @@ bool AsyncIO::asyncWrite(size_t qIdx, const void* buf, size_t length, off_t offs
   }
   ResetOverlapped(aio, DWORD(offset));
   m_maxBlock = std::max(m_maxBlock, qIdx + 1);
-  BOOL res = WriteFile(m_fh, buf, length, nullptr, &aio);
+  BOOL res = WriteFile(m_inner->m_fh, buf, length, nullptr, &aio);
   return res == TRUE || GetLastError() == ERROR_IO_PENDING;
 }
 
 ECardResult AsyncIO::pollStatus(size_t qIdx, SizeReturn* szRet) const {
-  auto& aio = const_cast<AsyncIO*>(this)->m_queue[qIdx];
+  auto& aio = m_inner->m_queue[qIdx];
   if (aio.first.hEvent == 0) {
     if (szRet)
       *szRet = aio.second;
     return ECardResult::READY;
   }
-  if (GetOverlappedResult(m_fh, &aio.first, &aio.second, FALSE)) {
+  if (GetOverlappedResult(m_inner->m_fh, &aio.first, &aio.second, FALSE)) {
     CloseHandle(aio.first.hEvent);
     aio.first.hEvent = 0;
     if (szRet)
@@ -124,12 +169,11 @@ ECardResult AsyncIO::pollStatus(size_t qIdx, SizeReturn* szRet) const {
 
 ECardResult AsyncIO::pollStatus() const {
   ECardResult result = ECardResult::READY;
-  for (auto it = const_cast<AsyncIO*>(this)->m_queue.begin();
-       it != const_cast<AsyncIO*>(this)->m_queue.begin() + m_maxBlock; ++it) {
+  for (auto it = m_inner->m_queue.begin(); it != m_inner->m_queue.begin() + m_maxBlock; ++it) {
     auto& aio = *it;
     if (aio.first.hEvent == 0)
       continue;
-    if (GetOverlappedResult(m_fh, &aio.first, &aio.second, FALSE)) {
+    if (GetOverlappedResult(m_inner->m_fh, &aio.first, &aio.second, FALSE)) {
       CloseHandle(aio.first.hEvent);
       aio.first.hEvent = 0;
     } else {
@@ -137,21 +181,30 @@ ECardResult AsyncIO::pollStatus() const {
         if (result > ECardResult::BUSY)
           result = ECardResult::BUSY;
       } else {
-        _waitForOperation(it - m_queue.cbegin());
+        _waitForOperation(it - m_inner->m_queue.cbegin());
         if (result > ECardResult::IOERROR)
           result = ECardResult::IOERROR;
       }
     }
   }
   if (result == ECardResult::READY)
-    const_cast<AsyncIO*>(this)->m_maxBlock = 0;
+    m_maxBlock = 0;
   return result;
 }
 
 void AsyncIO::waitForCompletion() const {
   for (size_t i = 0; i < m_maxBlock; ++i)
     _waitForOperation(i);
-  const_cast<AsyncIO*>(this)->m_maxBlock = 0;
+  m_maxBlock = 0;
 }
 
+void AsyncIO::resizeQueue(size_t queueSz) {
+  if (m_inner == nullptr) {
+    return;
+  }
+  m_inner->m_queue.resize(queueSz);
+}
+
+AsyncIO::operator bool() const { return m_inner != nullptr && m_inner->m_fh != INVALID_HANDLE_VALUE; }
+
 } // namespace kabufuda