diff --git a/README.md b/README.md
index 56016dc..fe797e1 100644
--- a/README.md
+++ b/README.md
@@ -152,6 +152,7 @@ Fine provides implementations for the following types:
 | `std::tuple<Args...>`                | x       | x       | `{a, b, ..., c}`            |
 | `std::vector<T>`                     | x       | x       | `list(a)`                   |
 | `std::map<K, V>`                     | x       | x       | `%{k => v}`                 |
+| `std::unordered_map<K, V>`           | x       | x       | `%{k => v}`                 |
 | `fine::ResourcePtr<T>`               | x       | x       | `reference`                 |
 | `T` with [struct metadata](#structs) | x       | x       | `%a{}`                      |
 | `fine::Ok<Args...>`                  | x       |         | `{:ok, ...}`                |
diff --git a/c_include/fine.hpp b/c_include/fine.hpp
index 5dca38f..7a31677 100644
--- a/c_include/fine.hpp
+++ b/c_include/fine.hpp
@@ -12,6 +12,7 @@
 #include <string>
 #include <string_view>
 #include <type_traits>
+#include <unordered_map>
 #include <variant>
 #include <vector>
 
@@ -652,6 +653,43 @@ struct Decoder<std::map<K, V, Compare, Alloc>> {
   };
 };
 
+template <typename K, typename V, typename Hash, typename Pred, typename Alloc>
+struct Decoder<std::unordered_map<K, V, Hash, Pred, Alloc>> {
+  static std::unordered_map<K, V, Hash, Pred, Alloc>
+  decode(ErlNifEnv *env, const ERL_NIF_TERM &term) {
+    std::unordered_map<K, V, Hash, Pred, Alloc> map;
+
+    ERL_NIF_TERM key_term, value_term;
+    ErlNifMapIterator iter;
+    if (!enif_map_iterator_create(env, term, &iter,
+                                  ERL_NIF_MAP_ITERATOR_FIRST)) {
+      throw std::invalid_argument("decode failed, expected a map");
+    }
+
+    // Define RAII cleanup for the iterator
+    auto cleanup = IterCleanup{env, iter};
+
+    while (enif_map_iterator_get_pair(env, &iter, &key_term, &value_term)) {
+      auto key = fine::decode<K>(env, key_term);
+      auto value = fine::decode<V>(env, value_term);
+
+      map.insert_or_assign(std::move(key), std::move(value));
+
+      enif_map_iterator_next(env, &iter);
+    }
+
+    return map;
+  }
+
+private:
+  struct IterCleanup {
+    ErlNifEnv *env;
+    ErlNifMapIterator iter;
+
+    ~IterCleanup() { enif_map_iterator_destroy(env, &iter); }
+  };
+};
+
 template <typename T> struct Decoder<ResourcePtr<T>> {
   static ResourcePtr<T> decode(ErlNifEnv *env, const ERL_NIF_TERM &term) {
     void *ptr;
@@ -875,10 +913,37 @@ struct Encoder<std::map<K, V, Compare, Alloc>> {
                              const std::map<K, V, Compare, Alloc> &map) {
     auto keys = std::vector<ERL_NIF_TERM>();
     auto values = std::vector<ERL_NIF_TERM>();
+    keys.reserve(map.size());
+    values.reserve(map.size());
+
+    for (const auto &[key, value] : map) {
+      keys.emplace_back(fine::encode(env, key));
+      values.emplace_back(fine::encode(env, value));
+    }
+
+    ERL_NIF_TERM map_term;
+    if (!enif_make_map_from_arrays(env, keys.data(), values.data(), keys.size(),
+                                   &map_term)) {
+      throw std::runtime_error("encode failed, failed to make a map");
+    }
+
+    return map_term;
+  }
+};
+
+template <typename K, typename V, typename Hash, typename Pred, typename Alloc>
+struct Encoder<std::unordered_map<K, V, Hash, Pred, Alloc>> {
+  static ERL_NIF_TERM
+  encode(ErlNifEnv *env,
+         const std::unordered_map<K, V, Hash, Pred, Alloc> &map) {
+    auto keys = std::vector<ERL_NIF_TERM>();
+    auto values = std::vector<ERL_NIF_TERM>();
+    keys.reserve(map.size());
+    values.reserve(map.size());
 
     for (const auto &[key, value] : map) {
-      keys.push_back(fine::encode(env, key));
-      values.push_back(fine::encode(env, value));
+      keys.emplace_back(fine::encode(env, key));
+      values.emplace_back(fine::encode(env, value));
     }
 
     ERL_NIF_TERM map_term;
@@ -1189,13 +1254,13 @@ inline int load(ErlNifEnv *env, void **, ERL_NIF_TERM) {
 
 namespace std {
 template <> struct hash<::fine::Term> {
-  size_t operator()(const ::fine::Term &term) noexcept {
+  size_t operator()(const ::fine::Term &term) const noexcept {
     return enif_hash(ERL_NIF_INTERNAL_HASH, term, 0);
   }
 };
 
 template <> struct hash<::fine::Atom> {
-  size_t operator()(const ::fine::Atom &atom) noexcept {
+  size_t operator()(const ::fine::Atom &atom) const noexcept {
     return std::hash<std::string_view>{}(atom.to_string());
   }
 };
diff --git a/test/c_src/finest.cpp b/test/c_src/finest.cpp
index cf91f7b..8f1f6d6 100644
--- a/test/c_src/finest.cpp
+++ b/test/c_src/finest.cpp
@@ -5,6 +5,7 @@
 #include <optional>
 #include <stdexcept>
 #include <thread>
+#include <unordered_map>
 
 #include <erl_nif.h>
 #include <fine.hpp>
@@ -216,6 +217,26 @@ codec_map_atom_int64_alloc(
 }
 FINE_NIF(codec_map_atom_int64_alloc, 0);
 
+std::unordered_map<fine::Atom, int64_t>
+codec_unordered_map_atom_int64(ErlNifEnv *,
+                               std::unordered_map<fine::Atom, int64_t> term) {
+  return term;
+}
+FINE_NIF(codec_unordered_map_atom_int64, 0);
+
+std::unordered_map<
+    fine::Atom, int64_t, std::hash<fine::Atom>, std::equal_to<fine::Atom>,
+    std::pmr::polymorphic_allocator<std::pair<const fine::Atom, int64_t>>>
+codec_unordered_map_atom_int64_alloc(
+    ErlNifEnv *,
+    std::unordered_map<
+        fine::Atom, int64_t, std::hash<fine::Atom>, std::equal_to<fine::Atom>,
+        std::pmr::polymorphic_allocator<std::pair<const fine::Atom, int64_t>>>
+        term) {
+  return term;
+}
+FINE_NIF(codec_unordered_map_atom_int64_alloc, 0);
+
 fine::ResourcePtr<TestResource>
 codec_resource(ErlNifEnv *, fine::ResourcePtr<TestResource> term) {
   return term;
diff --git a/test/lib/finest/nif.ex b/test/lib/finest/nif.ex
index d97279f..0e97d5d 100644
--- a/test/lib/finest/nif.ex
+++ b/test/lib/finest/nif.ex
@@ -38,6 +38,8 @@ defmodule Finest.NIF do
   def codec_vector_int64_alloc(_term), do: err!()
   def codec_map_atom_int64(_term), do: err!()
   def codec_map_atom_int64_alloc(_term), do: err!()
+  def codec_unordered_map_atom_int64(_term), do: err!()
+  def codec_unordered_map_atom_int64_alloc(_term), do: err!()
   def codec_resource(_term), do: err!()
   def codec_struct(_term), do: err!()
   def codec_struct_exception(_term), do: err!()
diff --git a/test/test/finest_test.exs b/test/test/finest_test.exs
index 26363ba..37a1a90 100644
--- a/test/test/finest_test.exs
+++ b/test/test/finest_test.exs
@@ -160,19 +160,76 @@ defmodule FinestTest do
     end
 
     test "map" do
-      assert NIF.codec_map_atom_int64(%{hello: 1, world: 2}) == %{hello: 1, world: 2}
-      assert NIF.codec_map_atom_int64_alloc(%{hello: 1, world: 2}) == %{hello: 1, world: 2}
+      small_map = %{hello: 1, world: 2}
+
+      empty_map = %{}
+
+      # Large maps have more than 32 elements:
+      #     https://www.erlang.org/doc/system/maps.html#how-large-maps-are-implemented
+      large_map =
+        0..64
+        |> Enum.with_index()
+        |> Map.new(fn {key, value} -> {:"a#{key}", value} end)
+
+      for map <- [small_map, empty_map, large_map] do
+        assert NIF.codec_map_atom_int64(map) == map
+        assert NIF.codec_map_atom_int64_alloc(map) == map
+        assert NIF.codec_unordered_map_atom_int64(map) == map
+        assert NIF.codec_unordered_map_atom_int64_alloc(map) == map
+      end
+
+      invalid_map = 10
+
+      assert_raise ArgumentError, "decode failed, expected a map", fn ->
+        NIF.codec_map_atom_int64(invalid_map)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected a map", fn ->
+        NIF.codec_map_atom_int64_alloc(invalid_map)
+      end
 
       assert_raise ArgumentError, "decode failed, expected a map", fn ->
-        NIF.codec_map_atom_int64(10)
+        NIF.codec_unordered_map_atom_int64(invalid_map)
       end
 
+      assert_raise ArgumentError, "decode failed, expected a map", fn ->
+        NIF.codec_unordered_map_atom_int64_alloc(invalid_map)
+      end
+
+      map_with_invalid_key = %{"hello" => 1}
+
       assert_raise ArgumentError, "decode failed, expected an atom", fn ->
-        NIF.codec_map_atom_int64(%{"hello" => 1})
+        NIF.codec_map_atom_int64(map_with_invalid_key)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected an atom", fn ->
+        NIF.codec_map_atom_int64_alloc(map_with_invalid_key)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected an atom", fn ->
+        NIF.codec_unordered_map_atom_int64(map_with_invalid_key)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected an atom", fn ->
+        NIF.codec_unordered_map_atom_int64_alloc(map_with_invalid_key)
+      end
+
+      map_with_invalid_value = %{hello: :world}
+
+      assert_raise ArgumentError, "decode failed, expected an integer", fn ->
+        NIF.codec_map_atom_int64(map_with_invalid_value)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected an integer", fn ->
+        NIF.codec_map_atom_int64_alloc(map_with_invalid_value)
+      end
+
+      assert_raise ArgumentError, "decode failed, expected an integer", fn ->
+        NIF.codec_unordered_map_atom_int64(map_with_invalid_value)
       end
 
       assert_raise ArgumentError, "decode failed, expected an integer", fn ->
-        NIF.codec_map_atom_int64(%{hello: 1.0})
+        NIF.codec_unordered_map_atom_int64_alloc(map_with_invalid_value)
       end
     end