diff --git a/include/spdlog/details/os-inl.h b/include/spdlog/details/os-inl.h
index 8fb2c7bc..f2570dc0 100644
--- a/include/spdlog/details/os-inl.h
+++ b/include/spdlog/details/os-inl.h
@@ -450,7 +450,7 @@ SPDLOG_INLINE void wstr_to_utf8buf(wstring_view_t wstr, memory_buf_t &target) {
     }
 
     int result_size = static_cast<int>(target.capacity());
-    if ((wstr_size + 1) * 2 > result_size) {
+    if ((wstr_size + 1) * 4 > result_size) {
         result_size =
             ::WideCharToMultiByte(CP_UTF8, 0, wstr.data(), wstr_size, NULL, 0, NULL, NULL);
     }