diff --git a/include/fmt/base.h b/include/fmt/base.h
index 87b3fd7c..ae3d43f4 100644
--- a/include/fmt/base.h
+++ b/include/fmt/base.h
@@ -2263,6 +2263,7 @@ template <typename Context> class value {
   }
 
   // Formats an argument of a custom type, such as a user-defined class.
+  // DEPRECATED! Formatter template parameter will be removed.
   template <typename T, typename Formatter>
   static void format_custom(void* arg, parse_context<char_type>& parse_ctx,
                             Context& ctx) {