diff --git a/include/fmt/format.h b/include/fmt/format.h
index 9b4f7357f550..77873c7f51e4 100644
--- a/include/fmt/format.h
+++ b/include/fmt/format.h
@@ -4428,7 +4428,7 @@ template <detail_exported::fixed_string Str> constexpr auto operator""_a() {
   return detail::udl_arg<char_t, sizeof(Str.data) / sizeof(char_t), Str>();
 }
 #  else
-constexpr auto operator"" _a(const char* s, size_t) -> detail::udl_arg<char> {
+constexpr auto operator""_a(const char* s, size_t) -> detail::udl_arg<char> {
   return {s};
 }
 #  endif