diff --git a/include/spdlog/sinks/rotating_file_sink-inl.h b/include/spdlog/sinks/rotating_file_sink-inl.h
index 6f10256f..bf9351eb 100644
--- a/include/spdlog/sinks/rotating_file_sink-inl.h
+++ b/include/spdlog/sinks/rotating_file_sink-inl.h
@@ -60,7 +60,7 @@ SPDLOG_INLINE filename_t rotating_file_sink<Mutex>::calc_filename(const filename
 
     filename_t basename, ext;
     std::tie(basename, ext) = details::file_helper::split_by_extension(filename);
-    return fmt_lib::format(SPDLOG_FILENAME_T("{}.{}{}"), basename, index, ext);
+    return fmt_lib::format(SPDLOG_FMT_STRING(SPDLOG_FILENAME_T("{}.{}{}")), basename, index, ext);
 }
 
 template <typename Mutex>