diff --git a/stl/src/tzdb.cpp b/stl/src/tzdb.cpp
index 8441519437..58f5ddd37d 100644
--- a/stl/src/tzdb.cpp
+++ b/stl/src/tzdb.cpp
@@ -200,6 +200,7 @@ namespace {
         const auto _Input_as_wchar = reinterpret_cast<const wchar_t*>(_Input);
         const auto _Count_result = __std_fs_convert_wide_to_narrow(_Code_page, _Input_as_wchar, _Input_len, nullptr, 0);
         if (_Count_result._Err != __std_win_error::_Success) {
+            SetLastError(static_cast<DWORD>(_Count_result._Err));
             _Err = __std_tzdb_error::_Win_error;
             return nullptr;
         }
@@ -214,6 +215,7 @@ namespace {
         const auto _Result =
             __std_fs_convert_wide_to_narrow(_Code_page, _Input_as_wchar, _Input_len, _Data.get(), _Count_result._Len);
         if (_Result._Err != __std_win_error::_Success) {
+            SetLastError(static_cast<DWORD>(_Result._Err));
             _Err = __std_tzdb_error::_Win_error;
             return nullptr;
         }