diff --git a/include/parselink/msgpack/core/packer.h b/include/parselink/msgpack/core/packer.h
index 807de66..6998ee6 100644
--- a/include/parselink/msgpack/core/packer.h
+++ b/include/parselink/msgpack/core/packer.h
@@ -66,17 +66,37 @@ public:
             , curr_(std::begin(buff_))
             , end_(std::end(buff_)) {}
 
+    struct context {
+        decltype(std::begin(BufferType{})) out;
+        decltype(std::begin(BufferType{})) end;
+
+        constexpr auto remaining() noexcept {
+            return std::ranges::distance(out, end);
+        }
+
+        template <packable_type T>
+        constexpr tl::expected<tl::monostate, error> pack(T&& v) noexcept {
+            using diff_type =
+                    std::iterator_traits<decltype(curr_)>::difference_type;
+            auto rem = remaining();
+            decltype(rem) needed = builtin_packer<T>::total_size(v);
+            if (needed > rem) {
+                return tl::make_unexpected(error::out_of_space);
+            } else {
+                builtin_packer<T>::pack(v, *this);
+                return tl::monostate{};
+            }
+        }
+    };
+
     template <packable_type T>
     constexpr tl::expected<tl::monostate, error> pack(T&& v) noexcept {
-        using diff_type =
-                std::iterator_traits<decltype(curr_)>::difference_type;
-        diff_type const space_needed = builtin_packer<T>::total_size(v);
-        if (space_needed > std::distance(curr_, end_)) {
-            return tl::make_unexpected(error::out_of_space);
-        } else {
-            curr_ = builtin_packer<T>::pack(v, curr_);
-            return tl::monostate{};
-        }
+        context ctx{curr_, end_};
+        // If packing is successful, it updates iterators.
+        return ctx.pack(std::forward<T>(v)).map([&]{
+            curr_ = ctx.out;
+            end_ = ctx.end;
+        });
     }
 
     constexpr auto tell() const noexcept {