diff --git a/include/magic_enum.hpp b/include/magic_enum.hpp
index 5b916be..9526b3c 100644
--- a/include/magic_enum.hpp
+++ b/include/magic_enum.hpp
@@ -914,23 +914,23 @@ template <typename E, typename BinaryPredicate = std::equal_to<char>>
 namespace fusion_detail {
 
 template <typename E>
-constexpr std::optional<std::uintmax_t> fuse_one_enum(std::optional<std::uintmax_t> hash, E value) noexcept {
+constexpr optional<std::uintmax_t> fuse_one_enum(optional<std::uintmax_t> hash, E value) noexcept {
   if (hash.has_value()) {
     if (const auto index = enum_index(value); index.has_value()) {
       // Add 1 to prevent matching 2D fusions with 3D fusions etc.
       return (hash.value() << detail::log2(enum_count<E>() + 1)) | (index.value() + 1);
     }
   }
-  return std::nullopt;
+  return {};
 }
 
 template <typename E>
-constexpr std::optional<std::uintmax_t> fuse_enum(E value) noexcept {
+constexpr optional<std::uintmax_t> fuse_enum(E value) noexcept {
   return fuse_one_enum(0, value);
 }
 
 template <typename E, typename... Es>
-constexpr std::optional<std::uintmax_t> fuse_enum(E head, Es... tail) noexcept {
+constexpr optional<std::uintmax_t> fuse_enum(E head, Es... tail) noexcept {
   return fuse_one_enum(fuse_enum(tail...), head);
 }