diff --git a/include/fmt/format.h b/include/fmt/format.h
index b6924f2b..67810188 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -1088,6 +1088,7 @@ template <typename Int> constexpr int digits10() FMT_NOEXCEPT {
 template <> constexpr int digits10<int128_t>() FMT_NOEXCEPT { return 38; }
 template <> constexpr int digits10<uint128_t>() FMT_NOEXCEPT { return 38; }
 
+// DEPRECATED! grouping will be merged into thousands_sep.
 template <typename Char> FMT_API std::string grouping_impl(locale_ref loc);
 template <typename Char> inline std::string grouping(locale_ref loc) {
   return grouping_impl<char>(loc);