diff --git a/headers/flat.hpp/flat_fwd.hpp b/headers/flat.hpp/flat_fwd.hpp
new file mode 100644
index 0000000..869022d
--- /dev/null
+++ b/headers/flat.hpp/flat_fwd.hpp
@@ -0,0 +1,44 @@
+/*******************************************************************************
+ * This file is part of the "https://github.com/blackmatov/flat.hpp"
+ * For conditions of distribution and use, see copyright notice in LICENSE.md
+ * Copyright (C) 2019, by Matvey Cherevko (blackmatov@gmail.com)
+ ******************************************************************************/
+
+#pragma once
+
+#include <vector>
+#include <cassert>
+#include <utility>
+#include <algorithm>
+#include <functional>
+#include <type_traits>
+#include <initializer_list>
+
+#include "detail/eq_compare.hpp"
+#include "detail/pair_compare.hpp"
+#include "detail/is_transparent.hpp"
+
+namespace flat_hpp
+{
+    template < typename Key
+             , typename Compare = std::less<Key>
+             , typename Container = std::vector<Key> >
+    class flat_set;
+
+    template < typename Key
+             , typename Compare = std::less<Key>
+             , typename Container = std::vector<Key> >
+    class flat_multiset;
+
+    template < typename Key
+             , typename Value
+             , typename Compare = std::less<Key>
+             , typename Container = std::vector<std::pair<Key, Value>> >
+    class flat_map;
+
+    template < typename Key
+             , typename Value
+             , typename Compare = std::less<Key>
+             , typename Container = std::vector<std::pair<Key, Value>> >
+    class flat_multimap;
+}
diff --git a/headers/flat.hpp/flat_map.hpp b/headers/flat.hpp/flat_map.hpp
index 0022533..c1a3679 100644
--- a/headers/flat.hpp/flat_map.hpp
+++ b/headers/flat.hpp/flat_map.hpp
@@ -6,25 +6,14 @@
 
 #pragma once
 
-#include <vector>
-#include <memory>
-#include <utility>
-#include <iterator>
-#include <algorithm>
-#include <functional>
-#include <type_traits>
-#include <initializer_list>
-
-#include "detail/eq_compare.hpp"
-#include "detail/pair_compare.hpp"
-#include "detail/is_transparent.hpp"
+#include "flat_fwd.hpp"
 
 namespace flat_hpp
 {
     template < typename Key
              , typename Value
-             , typename Compare = std::less<Key>
-             , typename Container = std::vector<std::pair<Key, Value>> >
+             , typename Compare
+             , typename Container >
     class flat_map
         : private detail::pair_compare<
             typename Container::value_type,
diff --git a/headers/flat.hpp/flat_multimap.hpp b/headers/flat.hpp/flat_multimap.hpp
index 77e0549..65bbc6b 100644
--- a/headers/flat.hpp/flat_multimap.hpp
+++ b/headers/flat.hpp/flat_multimap.hpp
@@ -6,25 +6,14 @@
 
 #pragma once
 
-#include <vector>
-#include <memory>
-#include <utility>
-#include <iterator>
-#include <algorithm>
-#include <functional>
-#include <type_traits>
-#include <initializer_list>
-
-#include "detail/eq_compare.hpp"
-#include "detail/pair_compare.hpp"
-#include "detail/is_transparent.hpp"
+#include "flat_fwd.hpp"
 
 namespace flat_hpp
 {
     template < typename Key
              , typename Value
-             , typename Compare = std::less<Key>
-             , typename Container = std::vector<std::pair<Key, Value>> >
+             , typename Compare
+             , typename Container >
     class flat_multimap
         : private detail::pair_compare<
             typename Container::value_type,
diff --git a/headers/flat.hpp/flat_multiset.hpp b/headers/flat.hpp/flat_multiset.hpp
index 577b9d0..2ecc8df 100644
--- a/headers/flat.hpp/flat_multiset.hpp
+++ b/headers/flat.hpp/flat_multiset.hpp
@@ -6,23 +6,13 @@
 
 #pragma once
 
-#include <vector>
-#include <memory>
-#include <utility>
-#include <iterator>
-#include <algorithm>
-#include <functional>
-#include <type_traits>
-#include <initializer_list>
-
-#include "detail/eq_compare.hpp"
-#include "detail/is_transparent.hpp"
+#include "flat_fwd.hpp"
 
 namespace flat_hpp
 {
     template < typename Key
-             , typename Compare = std::less<Key>
-             , typename Container = std::vector<Key> >
+             , typename Compare
+             , typename Container >
     class flat_multiset : private Compare {
         using base_type = Compare;
     public:
diff --git a/headers/flat.hpp/flat_set.hpp b/headers/flat.hpp/flat_set.hpp
index 7d0f27c..132ac9e 100644
--- a/headers/flat.hpp/flat_set.hpp
+++ b/headers/flat.hpp/flat_set.hpp
@@ -6,23 +6,13 @@
 
 #pragma once
 
-#include <vector>
-#include <memory>
-#include <utility>
-#include <iterator>
-#include <algorithm>
-#include <functional>
-#include <type_traits>
-#include <initializer_list>
-
-#include "detail/eq_compare.hpp"
-#include "detail/is_transparent.hpp"
+#include "flat_fwd.hpp"
 
 namespace flat_hpp
 {
     template < typename Key
-             , typename Compare = std::less<Key>
-             , typename Container = std::vector<Key> >
+             , typename Compare
+             , typename Container >
     class flat_set : private Compare {
         using base_type = Compare;
     public: