diff --git a/include/fmt/format.h b/include/fmt/format.h
index 51aff51beefab..5808635b0eb41 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -3583,6 +3583,10 @@ template <typename Char> struct arg_formatter {
   const format_specs<Char>& specs;
   locale_ref locale;
 
+  arg_formatter(buffer_appender<Char> it, const format_specs<Char>& s,
+                locale_ref l)
+      : out{it}, specs{s}, locale{l} {}
+
   template <typename T>
   FMT_CONSTEXPR FMT_INLINE auto operator()(T value) -> iterator {
     return detail::write(out, value, specs, locale);