diff --git a/include/spdlog/common.h b/include/spdlog/common.h
index ae9f0fa4..2f23e9e4 100644
--- a/include/spdlog/common.h
+++ b/include/spdlog/common.h
@@ -26,11 +26,6 @@
 #include <windows.h>
 #endif //_WIN32
 
-#if defined(SPDLOG_WCHAR_FILENAMES) || defined(SPDLOG_WCHAR_TO_UTF8_SUPPORT)
-#include <codecvt>
-#include <locale>
-#endif
-
 #ifdef SPDLOG_COMPILED_LIB
 #undef SPDLOG_HEADER_ONLY
 #define SPDLOG_INLINE
@@ -80,11 +75,6 @@ class sink;
 #if defined(_WIN32) && defined(SPDLOG_WCHAR_FILENAMES)
 using filename_t = std::wstring;
 #define SPDLOG_FILENAME_T(s) L##s
-inline std::string filename_to_str(const filename_t &filename)
-{
-    std::wstring_convert<std::codecvt_utf8<wchar_t>, wchar_t> c;
-    return c.to_bytes(filename);
-}
 #else
 using filename_t = std::string;
 #define SPDLOG_FILENAME_T(s) s
@@ -97,10 +87,13 @@ using err_handler = std::function<void(const std::string &err_msg)>;
 
 // string_view type - either std::string_view or fmt::string_view (pre c++17)
 #if defined(FMT_USE_STD_STRING_VIEW)
-using string_view_t = std::string_view;
+template<typename T>
+using basic_string_view_t = std::basic_string_view<T>;
 #else
-using string_view_t = fmt::string_view;
+template<typename T>
+using basic_string_view_t = fmt::basic_string_view<T>;
 #endif
+using string_view_t = basic_string_view_t<char>;
 
 #if defined(SPDLOG_NO_ATOMIC_LEVELS)
 using level_t = details::null_atomic_int;
diff --git a/include/spdlog/details/os-inl.h b/include/spdlog/details/os-inl.h
index e0809d9b..0675436b 100644
--- a/include/spdlog/details/os-inl.h
+++ b/include/spdlog/details/os-inl.h
@@ -36,6 +36,10 @@
 #include <share.h>
 #endif
 
+#if defined(SPDLOG_WCHAR_TO_UTF8_SUPPORT) || defined(SPDLOG_WCHAR_FILENAMES)
+#include <limits>
+#endif
+
 #else // unix
 
 #include <fcntl.h>
@@ -342,13 +346,14 @@ SPDLOG_INLINE void sleep_for_millis(int milliseconds) SPDLOG_NOEXCEPT
 
 // wchar support for windows file names (SPDLOG_WCHAR_FILENAMES must be defined)
 #if defined(_WIN32) && defined(SPDLOG_WCHAR_FILENAMES)
-SPDLOG_INLINE std::string filename_to_str(const filename_t &filename) SPDLOG_NOEXCEPT
+SPDLOG_INLINE std::string filename_to_str(const filename_t &filename)
 {
-    std::wstring_convert<std::codecvt_utf8<wchar_t>, wchar_t> c;
-    return c.to_bytes(filename);
+    fmt::memory_buffer buf;
+    wstr_to_utf8buf(filename, buf);
+    return fmt::to_string(buf);
 }
 #else
-SPDLOG_INLINE std::string filename_to_str(const filename_t &filename) SPDLOG_NOEXCEPT
+SPDLOG_INLINE std::string filename_to_str(const filename_t &filename)
 {
     return filename;
 }
@@ -398,28 +403,42 @@ SPDLOG_INLINE bool in_terminal(FILE *file) SPDLOG_NOEXCEPT
 #endif
 }
 
-#if defined(SPDLOG_WCHAR_TO_UTF8_SUPPORT) && defined(_WIN32)
-SPDLOG_INLINE void wbuf_to_utf8buf(const fmt::wmemory_buffer &wbuf, fmt::memory_buffer &target)
+#if (defined(SPDLOG_WCHAR_TO_UTF8_SUPPORT) || defined(SPDLOG_WCHAR_FILENAMES)) && defined(_WIN32)
+SPDLOG_INLINE void wstr_to_utf8buf(basic_string_view_t<wchar_t> wstr, fmt::memory_buffer &target)
 {
-    int wbuf_size = static_cast<int>(wbuf.size());
-    if (wbuf_size == 0)
+    if (wstr.size() > static_cast<size_t>(std::numeric_limits<int>::max()))
     {
+        throw spdlog::spdlog_ex("UTF-16 string is too big to be converted to UTF-8");
+    }
+
+    int wstr_size = static_cast<int>(wstr.size());
+    if (wstr_size == 0)
+    {
+        target.resize(0);
         return;
     }
 
-    auto result_size = ::WideCharToMultiByte(CP_UTF8, 0, wbuf.data(), wbuf_size, NULL, 0, NULL, NULL);
+    int result_size = static_cast<int>(target.capacity());
+    if ((wstr_size + 1) * 2 > result_size)
+    {
+        result_size = ::WideCharToMultiByte(CP_UTF8, 0, wstr.data(), wstr_size, NULL, 0, NULL, NULL);
+    }
 
     if (result_size > 0)
     {
         target.resize(result_size);
-        ::WideCharToMultiByte(CP_UTF8, 0, wbuf.data(), wbuf_size, &target.data()[0], result_size, NULL, NULL);
-    }
-    else
-    {
-        throw spdlog::spdlog_ex(fmt::format("WideCharToMultiByte failed. Last error: {}", ::GetLastError()));
+        result_size = ::WideCharToMultiByte(CP_UTF8, 0, wstr.data(), wstr_size, target.data(), result_size, NULL, NULL);
+
+        if (result_size > 0)
+        {
+            target.resize(result_size);
+            return;
+        }
     }
+
+    throw spdlog::spdlog_ex(fmt::format("WideCharToMultiByte failed. Last error: {}", ::GetLastError()));
 }
-#endif // SPDLOG_WCHAR_TO_UTF8_SUPPORT) && _WIN32
+#endif // (defined(SPDLOG_WCHAR_TO_UTF8_SUPPORT) || defined(SPDLOG_WCHAR_FILENAMES)) && defined(_WIN32)
 
 } // namespace os
 } // namespace details
diff --git a/include/spdlog/details/os.h b/include/spdlog/details/os.h
index 4afe0cb9..27694494 100644
--- a/include/spdlog/details/os.h
+++ b/include/spdlog/details/os.h
@@ -68,7 +68,7 @@ size_t thread_id() SPDLOG_NOEXCEPT;
 // See https://github.com/gabime/spdlog/issues/609
 void sleep_for_millis(int milliseconds) SPDLOG_NOEXCEPT;
 
-std::string filename_to_str(const filename_t &filename) SPDLOG_NOEXCEPT;
+std::string filename_to_str(const filename_t &filename);
 
 int pid() SPDLOG_NOEXCEPT;
 
@@ -80,8 +80,8 @@ bool is_color_terminal() SPDLOG_NOEXCEPT;
 // Source: https://github.com/agauniyal/rang/
 bool in_terminal(FILE *file) SPDLOG_NOEXCEPT;
 
-#if defined(SPDLOG_WCHAR_TO_UTF8_SUPPORT) && defined(_WIN32)
-void wbuf_to_utf8buf(const fmt::wmemory_buffer &wbuf, fmt::memory_buffer &target);
+#if (defined(SPDLOG_WCHAR_TO_UTF8_SUPPORT) || defined(SPDLOG_WCHAR_FILENAMES)) && defined(_WIN32)
+void wstr_to_utf8buf(basic_string_view_t<wchar_t> wstr, fmt::memory_buffer &target);
 #endif
 
 } // namespace os
diff --git a/include/spdlog/logger.h b/include/spdlog/logger.h
index bc627c4b..1d831362 100644
--- a/include/spdlog/logger.h
+++ b/include/spdlog/logger.h
@@ -243,8 +243,10 @@ public:
             // format to wmemory_buffer and convert to utf8
             fmt::wmemory_buffer wbuf;
             fmt::format_to(wbuf, fmt, args...);
+
             fmt::memory_buffer buf;
-            details::os::wbuf_to_utf8buf(wbuf, buf);
+            details::os::wstr_to_utf8buf(basic_string_view_t<wchar_t>(wbuf.data(), wbuf.size()), buf);
+
             details::log_msg log_msg(source, name_, lvl, string_view_t(buf.data(), buf.size()));
             sink_it_(log_msg);
         }