diff --git a/include/spdlog/fmt/bundled/format.h b/include/spdlog/fmt/bundled/format.h
index 60dd3839..3cd25425 100644
--- a/include/spdlog/fmt/bundled/format.h
+++ b/include/spdlog/fmt/bundled/format.h
@@ -73,9 +73,9 @@
 #endif  // FMT_MODULE
 
 #if (defined(__GNUC__) && __GNUC__ < 5)
-#  define OPERATOR_LITERAL(suffix) operator"" suffix
+#  define OPERATOR_LITERAL(suffix) operator"" _suffix
 #else
-#  define OPERATOR_LITERAL(suffix) operator""suffix
+#  define OPERATOR_LITERAL(suffix) operator""_suffix
 #endif
 
 #if defined(FMT_USE_NONTYPE_TEMPLATE_ARGS)
@@ -3999,7 +3999,7 @@ template <typename T, typename Char = char> struct nested_formatter {
 
 inline namespace literals {
 #if FMT_USE_NONTYPE_TEMPLATE_ARGS
-template <detail::fixed_string S> constexpr auto OPERATOR_LITERAL(_a)() {
+template <detail::fixed_string S> constexpr auto OPERATOR_LITERAL(a)() {
   using char_t = remove_cvref_t<decltype(*S.data)>;
   return detail::udl_arg<char_t, sizeof(S.data) / sizeof(char_t), S>();
 }
@@ -4012,7 +4012,7 @@ template <detail::fixed_string S> constexpr auto OPERATOR_LITERAL(_a)() {
  *     using namespace fmt::literals;
  *     fmt::print("The answer is {answer}.", "answer"_a=42);
  */
-constexpr auto OPERATOR_LITERAL(_a)(const char* s, size_t) -> detail::udl_arg<char> {
+constexpr auto OPERATOR_LITERAL(a)(const char* s, size_t) -> detail::udl_arg<char> {
   return {s};
 }
 #endif  // FMT_USE_NONTYPE_TEMPLATE_ARGS