diff --git a/source/mijin/container/optional.hpp b/source/mijin/container/optional.hpp
index da39933..c3bd31d 100644
--- a/source/mijin/container/optional.hpp
+++ b/source/mijin/container/optional.hpp
@@ -157,8 +157,21 @@ public:
     [[nodiscard]] constexpr bool empty() const noexcept { return storage_.empty(); }
     inline void reset() noexcept;
 
+
+    template<typename TCallable, typename TErrorCallable = int>
+    auto then(TCallable&& onSuccess, TErrorCallable&& onError = 0)
+    {
+        return thenImpl(*this, std::forward<TCallable>(onSuccess), std::forward<TErrorCallable>(onError));
+    }
+
+    template<typename TCallable, typename TErrorCallable = int>
+    auto then(TCallable&& onSuccess, TErrorCallable&& onError = 0) const
+    {
+        return thenImpl(*this, std::forward<TCallable>(onSuccess), std::forward<TErrorCallable>(onError));
+    }
+private:
     template<typename TSelf, typename TCallable, typename TErrorCallable = int>
-    auto then(this TSelf&& self, TCallable&& onSuccess, TErrorCallable&& onError = 0)
+    static auto thenImpl(TSelf&& self, TCallable&& onSuccess, TErrorCallable&& onError = 0)
     {
         using result_t = std::invoke_result_t<TCallable, std::add_rvalue_reference_t<TValue>>;