diff --git a/fuzzing/0000.write/c_file_unlocked.cc b/fuzzing/0000.write/c_file_unlocked.cc
index a83b1e019..070982471 100644
--- a/fuzzing/0000.write/c_file_unlocked.cc
+++ b/fuzzing/0000.write/c_file_unlocked.cc
@@ -1,9 +1,17 @@
 #include <fast_io.h>
 
-fast_io::c_file_unlocked obf("/dev/null", fast_io::open_mode::out);
+fast_io::c_file_unlocked obf(
+#if defined(_WIN32) && !defined(__WINE__)
+	"nul"
+#else
+	"/dev/null"
+#endif
+	,
+	fast_io::open_mode::out);
 
-extern "C" int LLVMFuzzerTestOneInput(std::uint8_t const *ptr, std::size_t n) noexcept
+extern "C" int LLVMFuzzerTestOneInput(std::uint8_t const *pptr, std::size_t n) noexcept
 {
-	write(obf, ptr, ptr + n);
+	::std::byte const *ptr{reinterpret_cast<::std::byte const *>(pptr)};
+	::fast_io::operations::write_all_bytes(obf, ptr, ptr + n);
 	return 0;
-}
\ No newline at end of file
+}
diff --git a/fuzzing/0000.write/filebuf_file.cc b/fuzzing/0000.write/filebuf_file.cc
new file mode 100644
index 000000000..68cbcf7a5
--- /dev/null
+++ b/fuzzing/0000.write/filebuf_file.cc
@@ -0,0 +1,21 @@
+#include <fast_io.h>
+#include <fast_io_legacy.h>
+
+fast_io::filebuf_file obf(
+#if defined(_WIN32) && !defined(__WINE__)
+	"nul"
+#else
+	"/dev/null"
+#endif
+	,
+	fast_io::open_mode::out);
+
+
+extern "C" int LLVMFuzzerTestOneInput(std::uint8_t const *pptr, std::size_t n) noexcept
+{
+	char const *ptr{reinterpret_cast<char const *>(pptr)};
+	using namespace fast_io::mnp;
+	::fast_io::operations::write_all(obf, ptr, ptr + n);
+
+	return 0;
+}
diff --git a/fuzzing/0000.write/u32c_file_unlocked.cc b/fuzzing/0000.write/u32c_file_unlocked.cc
new file mode 100644
index 000000000..c26c81136
--- /dev/null
+++ b/fuzzing/0000.write/u32c_file_unlocked.cc
@@ -0,0 +1,24 @@
+#include <fast_io.h>
+
+fast_io::u32c_file_unlocked obf(
+#if defined(_WIN32) && !defined(__WINE__)
+	"nul"
+#else
+	"/dev/null"
+#endif
+	,
+	fast_io::open_mode::out);
+
+extern "C"
+	[[__gnu__::__weak__]]
+	uintptr_t __sancov_lowest_stack{};
+
+extern "C" int LLVMFuzzerTestOneInput(std::uint8_t const *pptr, std::size_t n) noexcept
+{
+	using chartype = char32_t;
+	char32_t const *ptr{reinterpret_cast<char32_t const *>(pptr)};
+	using namespace fast_io::mnp;
+	::fast_io::operations::write_all(obf, ptr, ptr + n / sizeof(char32_t));
+
+	return 0;
+}
diff --git a/fuzzing/0000.write/wc_file_unlocked.cc b/fuzzing/0000.write/wc_file_unlocked.cc
new file mode 100644
index 000000000..e1bf3c476
--- /dev/null
+++ b/fuzzing/0000.write/wc_file_unlocked.cc
@@ -0,0 +1,34 @@
+#include <fast_io.h>
+
+fast_io::wc_file_unlocked obf(
+#if defined(_WIN32) && !defined(__WINE__)
+	"nul"
+#else
+	"/dev/null"
+#endif
+	,
+	fast_io::open_mode::out);
+
+extern "C"
+	[[__gnu__::__weak__]]
+	uintptr_t __sancov_lowest_stack{};
+
+struct usefwide
+{
+	usefwide()
+	{
+		fwide(obf.fp, 1);
+	}
+};
+#ifdef USE_FWIDE
+usefwide t;
+#endif
+
+extern "C" int LLVMFuzzerTestOneInput(std::uint8_t const *pptr, std::size_t n) noexcept
+{
+	wchar_t const *ptr{reinterpret_cast<wchar_t const *>(pptr)};
+	using namespace fast_io::mnp;
+	::fast_io::operations::write_all(obf, ptr, ptr + n / sizeof(wchar_t));
+
+	return 0;
+}
diff --git a/fuzzing/0000.write/wfilebuf_file.cc b/fuzzing/0000.write/wfilebuf_file.cc
new file mode 100644
index 000000000..9192be423
--- /dev/null
+++ b/fuzzing/0000.write/wfilebuf_file.cc
@@ -0,0 +1,21 @@
+#include <fast_io.h>
+#include <fast_io_legacy.h>
+
+fast_io::wfilebuf_file obf(
+#if defined(_WIN32) && !defined(__WINE__)
+	"nul"
+#else
+	"/dev/null"
+#endif
+	,
+	fast_io::open_mode::out);
+
+
+extern "C" int LLVMFuzzerTestOneInput(std::uint8_t const *pptr, std::size_t n) noexcept
+{
+	wchar_t const *ptr{reinterpret_cast<wchar_t const *>(pptr)};
+	using namespace fast_io::mnp;
+	::fast_io::operations::write_all(obf, ptr, ptr + n / sizeof(wchar_t));
+
+	return 0;
+}
diff --git a/include/fast_io_legacy_impl/c/wincrt.h b/include/fast_io_legacy_impl/c/wincrt.h
index 11cf07b31..066e64740 100644
--- a/include/fast_io_legacy_impl/c/wincrt.h
+++ b/include/fast_io_legacy_impl/c/wincrt.h
@@ -372,16 +372,15 @@ inline T *wincrt_get_buffer_ptr_impl(FILE *__restrict fpp) noexcept
 	}
 }
 
-template <typename T>
 inline void wincrt_set_buffer_curr_ptr_impl(FILE *__restrict fpp,
 #if __has_cpp_attribute(__gnu__::__may_alias__)
 											[[__gnu__::__may_alias__]]
 #endif
-											T *ptr) noexcept
+											void *ptr) noexcept
 {
 	crt_iobuf *fp{reinterpret_cast<crt_iobuf *>(fpp)};
 	fp->_cnt -= static_cast<::std::int_least32_t>(
-		static_cast<::std::uint_least32_t>(static_cast<::std::size_t>(reinterpret_cast<char *>(ptr) - fp->_ptr) / sizeof(T)));
+		static_cast<::std::uint_least32_t>(static_cast<::std::size_t>(reinterpret_cast<char *>(ptr) - fp->_ptr)));
 	fp->_ptr = reinterpret_cast<char *>(ptr);
 }
 #if defined(_MSC_VER) || defined(_UCRT)