diff --git a/src/alias_registry.hh b/src/alias_registry.hh
index ae879eef..e2d4e271 100644
--- a/src/alias_registry.hh
+++ b/src/alias_registry.hh
@@ -1,7 +1,6 @@
 #ifndef alias_registry_hh_INCLUDED
 #define alias_registry_hh_INCLUDED
 
-#include "utils.hh"
 #include "safe_ptr.hh"
 #include "string.hh"
 
diff --git a/src/buffer.hh b/src/buffer.hh
index 4715ddc1..ebb3eed7 100644
--- a/src/buffer.hh
+++ b/src/buffer.hh
@@ -9,9 +9,6 @@
 #include "value.hh"
 
 #include <vector>
-#include <list>
-#include <memory>
-#include <unordered_set>
 
 namespace Kakoune
 {
diff --git a/src/client.hh b/src/client.hh
index 6da499a3..ebbc96e8 100644
--- a/src/client.hh
+++ b/src/client.hh
@@ -5,7 +5,6 @@
 #include "env_vars.hh"
 #include "input_handler.hh"
 #include "safe_ptr.hh"
-#include "string.hh"
 #include "utils.hh"
 #include "option_manager.hh"
 
@@ -14,6 +13,7 @@ namespace Kakoune
 
 class UserInterface;
 class Window;
+class String;
 
 class Client : public SafeCountable, public OptionManagerWatcher
 {
diff --git a/src/color.cc b/src/color.cc
index d056fb25..8f1b01c1 100644
--- a/src/color.cc
+++ b/src/color.cc
@@ -3,6 +3,8 @@
 #include "exception.hh"
 #include "regex.hh"
 
+#include <cstdio>
+
 namespace Kakoune
 {
 
diff --git a/src/color.hh b/src/color.hh
index f6b3e842..1de59fcd 100644
--- a/src/color.hh
+++ b/src/color.hh
@@ -1,8 +1,6 @@
 #ifndef color_hh_INCLUDED
 #define color_hh_INCLUDED
 
-#include <utility>
-
 namespace Kakoune
 {
 
diff --git a/src/debug.cc b/src/debug.cc
index 6d865013..c59a9802 100644
--- a/src/debug.cc
+++ b/src/debug.cc
@@ -3,6 +3,7 @@
 #include "assert.hh"
 #include "buffer.hh"
 #include "buffer_manager.hh"
+#include "string.hh"
 
 namespace Kakoune
 {
diff --git a/src/debug.hh b/src/debug.hh
index 26b94820..02e46708 100644
--- a/src/debug.hh
+++ b/src/debug.hh
@@ -1,11 +1,11 @@
 #ifndef debug_hh_INCLUDED
 #define debug_hh_INCLUDED
 
-#include "string.hh"
-
 namespace Kakoune
 {
 
+class StringView;
+
 void write_debug(StringView str);
 
 }
diff --git a/src/display_buffer.cc b/src/display_buffer.cc
index af8d15e4..a56fe612 100644
--- a/src/display_buffer.cc
+++ b/src/display_buffer.cc
@@ -1,10 +1,48 @@
 #include "display_buffer.hh"
 
 #include "assert.hh"
+#include "buffer.hh"
+#include "utf8.hh"
 
 namespace Kakoune
 {
 
+StringView DisplayAtom::content() const
+{
+    switch (m_type)
+    {
+        case BufferRange:
+        {
+            auto line = (*m_buffer)[m_begin.line];
+            if (m_begin.line == m_end.line)
+                return line.substr(m_begin.column, m_end.column - m_begin.column);
+            else if (m_begin.line+1 == m_end.line and m_end.column == 0)
+                return line.substr(m_begin.column);
+            break;
+        }
+        case Text:
+        case ReplacedBufferRange:
+            return m_text;
+    }
+    kak_assert(false);
+    return {};
+}
+
+CharCount DisplayAtom::length() const
+{
+    switch (m_type)
+    {
+        case BufferRange:
+           return utf8::distance(m_buffer->iterator_at(m_begin),
+                                 m_buffer->iterator_at(m_end));
+        case Text:
+        case ReplacedBufferRange:
+           return m_text.char_length();
+    }
+    kak_assert(false);
+    return 0;
+}
+
 void DisplayAtom::trim_begin(CharCount count)
 {
     if (m_type == BufferRange)
diff --git a/src/display_buffer.hh b/src/display_buffer.hh
index 8ad01661..83ba7d6b 100644
--- a/src/display_buffer.hh
+++ b/src/display_buffer.hh
@@ -1,17 +1,17 @@
 #ifndef display_buffer_hh_INCLUDED
 #define display_buffer_hh_INCLUDED
 
-#include "buffer.hh"
 #include "face.hh"
 #include "coord.hh"
 #include "string.hh"
-#include "utf8.hh"
 
 #include <vector>
 
 namespace Kakoune
 {
 
+class Buffer;
+
 struct DisplayAtom
 {
 public:
@@ -25,41 +25,8 @@ public:
         : m_type(Text), m_text(std::move(str)), face(face)
      { check_invariant(); }
 
-    StringView content() const
-    {
-        switch (m_type)
-        {
-            case BufferRange:
-            {
-                auto line = (*m_buffer)[m_begin.line];
-                if (m_begin.line == m_end.line)
-                    return line.substr(m_begin.column, m_end.column - m_begin.column);
-                else if (m_begin.line+1 == m_end.line and m_end.column == 0)
-                    return line.substr(m_begin.column);
-                break;
-            }
-            case Text:
-            case ReplacedBufferRange:
-                return m_text;
-        }
-        kak_assert(false);
-        return {};
-    }
-
-    CharCount length() const
-    {
-        switch (m_type)
-        {
-            case BufferRange:
-               return utf8::distance(m_buffer->iterator_at(m_begin),
-                                     m_buffer->iterator_at(m_end));
-            case Text:
-            case ReplacedBufferRange:
-               return m_text.char_length();
-        }
-        kak_assert(false);
-        return 0;
-    }
+    StringView content() const;
+    CharCount length() const;
 
     const ByteCoord& begin() const
     {
diff --git a/src/env_vars.cc b/src/env_vars.cc
index 7a759399..f89fe7ff 100644
--- a/src/env_vars.cc
+++ b/src/env_vars.cc
@@ -1,5 +1,7 @@
 #include "env_vars.hh"
 
+#include "string.hh"
+
 extern char **environ;
 
 namespace Kakoune
diff --git a/src/env_vars.hh b/src/env_vars.hh
index 087d51a7..89d3459e 100644
--- a/src/env_vars.hh
+++ b/src/env_vars.hh
@@ -1,13 +1,12 @@
 #ifndef env_vars_hh_INCLUDED
 #define env_vars_hh_INCLUDED
 
-#include "string.hh"
-
 #include <unordered_map>
 
 namespace Kakoune
 {
 
+class String;
 using EnvVarMap = std::unordered_map<String, String>;
 
 EnvVarMap get_env_vars();
@@ -15,4 +14,3 @@ EnvVarMap get_env_vars();
 }
 
 #endif // env_vars_hh_INCLUDED
-
diff --git a/src/file.cc b/src/file.cc
index 19f2a764..472d3fb9 100644
--- a/src/file.cc
+++ b/src/file.cc
@@ -8,6 +8,7 @@
 #include "debug.hh"
 #include "unicode.hh"
 #include "regex.hh"
+#include "string.hh"
 
 #include <errno.h>
 #include <sys/types.h>
diff --git a/src/file.hh b/src/file.hh
index 99bb3715..8cef4473 100644
--- a/src/file.hh
+++ b/src/file.hh
@@ -2,7 +2,6 @@
 #define file_hh_INCLUDED
 
 #include "exception.hh"
-#include "string.hh"
 #include "regex.hh"
 
 namespace Kakoune
@@ -23,6 +22,9 @@ struct file_not_found : file_access_error
 };
 
 class Buffer;
+template<typename T> class memoryview;
+class String;
+class StringView;
 
 // parse ~/ and $env values in filename and returns the translated filename
 String parse_filename(StringView filename);
diff --git a/src/hook_manager.hh b/src/hook_manager.hh
index 21aade05..93a67ef7 100644
--- a/src/hook_manager.hh
+++ b/src/hook_manager.hh
@@ -2,7 +2,6 @@
 #define hook_manager_hh_INCLUDED
 
 #include "id_map.hh"
-#include "utils.hh"
 
 #include <unordered_map>
 
diff --git a/src/keymap_manager.cc b/src/keymap_manager.cc
index 71f936fd..0d376a1b 100644
--- a/src/keymap_manager.cc
+++ b/src/keymap_manager.cc
@@ -1,5 +1,7 @@
 #include "keymap_manager.hh"
 
+#include "memoryview.hh"
+
 namespace std
 {
 
diff --git a/src/keymap_manager.hh b/src/keymap_manager.hh
index 6521f69c..b6b0bf52 100644
--- a/src/keymap_manager.hh
+++ b/src/keymap_manager.hh
@@ -5,6 +5,7 @@
 #include "utils.hh"
 
 #include <unordered_map>
+#include <vector>
 
 namespace Kakoune
 {
@@ -20,6 +21,8 @@ enum class KeymapMode : int
     View,
 };
 
+template<typename T> class memoryview;
+
 class KeymapManager
 {
 public:
diff --git a/src/keys.hh b/src/keys.hh
index d579395d..3123f7cc 100644
--- a/src/keys.hh
+++ b/src/keys.hh
@@ -1,8 +1,8 @@
 #ifndef keys_hh_INCLUDED
 #define keys_hh_INCLUDED
 
-#include "string.hh"
 #include "unicode.hh"
+#include "flags.hh"
 
 #include <vector>
 
@@ -64,8 +64,13 @@ struct Key
     { return modifiers != other.modifiers or key != other.key; }
 };
 
+template<> struct WithBitOps<Key::Modifiers> : std::true_type {};
+
 using KeyList = std::vector<Key>;
 
+class String;
+class StringView;
+
 KeyList parse_keys(StringView str);
 String  key_to_str(Key key);
 
@@ -79,7 +84,7 @@ namespace std
 {
 
 template<>
-struct hash<Kakoune::Key> : unary_function<const Kakoune::Key&, size_t>
+struct hash<Kakoune::Key>
 {
     size_t operator()(Kakoune::Key key) const
     {
diff --git a/src/ncurses.cc b/src/ncurses.cc
index c479d66a..de72f320 100644
--- a/src/ncurses.cc
+++ b/src/ncurses.cc
@@ -2,6 +2,7 @@
 
 #include "display_buffer.hh"
 #include "event_manager.hh"
+#include "keys.hh"
 #include "register_manager.hh"
 #include "utf8_iterator.hh"
 
diff --git a/src/ncurses.hh b/src/ncurses.hh
index 3f59b05c..23d91f5c 100644
--- a/src/ncurses.hh
+++ b/src/ncurses.hh
@@ -1,8 +1,9 @@
 #ifndef ncurses_hh_INCLUDED
 #define ncurses_hh_INCLUDED
 
-#include "display_buffer.hh"
+#include "coord.hh"
 #include "event_manager.hh"
+#include "face.hh"
 #include "user_interface.hh"
 
 namespace Kakoune
diff --git a/src/option_types.hh b/src/option_types.hh
index f7f372fb..b304f12b 100644
--- a/src/option_types.hh
+++ b/src/option_types.hh
@@ -5,6 +5,7 @@
 #include "string.hh"
 #include "units.hh"
 #include "coord.hh"
+#include "memoryview.hh"
 
 #include <tuple>
 #include <vector>
diff --git a/src/remote.hh b/src/remote.hh
index 90aa14da..0d85cf81 100644
--- a/src/remote.hh
+++ b/src/remote.hh
@@ -1,9 +1,13 @@
 #ifndef remote_hh_INCLUDED
 #define remote_hh_INCLUDED
 
-#include "display_buffer.hh"
-#include "user_interface.hh"
+#include "coord.hh"
 #include "env_vars.hh"
+#include "exception.hh"
+#include "user_interface.hh"
+#include "utils.hh"
+
+#include <memory>
 
 namespace Kakoune
 {
diff --git a/src/shell_manager.hh b/src/shell_manager.hh
index e2af4241..8b930777 100644
--- a/src/shell_manager.hh
+++ b/src/shell_manager.hh
@@ -1,7 +1,6 @@
 #ifndef shell_manager_hh_INCLUDED
 #define shell_manager_hh_INCLUDED
 
-#include "string.hh"
 #include "regex.hh"
 #include "utils.hh"
 #include "env_vars.hh"
@@ -10,6 +9,10 @@ namespace Kakoune
 {
 
 class Context;
+template<typename T> class memoryview;
+class String;
+class StringView;
+
 using EnvVarRetriever = std::function<String (StringView name, const Context&)>;
 
 class ShellManager : public Singleton<ShellManager>
diff --git a/src/string.hh b/src/string.hh
index f7311d9d..55276d73 100644
--- a/src/string.hh
+++ b/src/string.hh
@@ -1,13 +1,13 @@
 #ifndef string_hh_INCLUDED
 #define string_hh_INCLUDED
 
-#include "memoryview.hh"
 #include "units.hh"
 #include "utf8.hh"
 
 #include <string>
 #include <climits>
 #include <cstring>
+#include <vector>
 
 namespace Kakoune
 {
diff --git a/src/user_interface.hh b/src/user_interface.hh
index dc415967..43d10377 100644
--- a/src/user_interface.hh
+++ b/src/user_interface.hh
@@ -1,11 +1,9 @@
 #ifndef user_interface_hh_INCLUDED
 #define user_interface_hh_INCLUDED
 
-#include "color.hh"
-#include "keys.hh"
-#include "memoryview.hh"
 #include "safe_ptr.hh"
 
+#include <functional>
 #include <unordered_map>
 
 namespace Kakoune
@@ -15,6 +13,9 @@ class String;
 class DisplayBuffer;
 class DisplayLine;
 struct CharCoord;
+struct Face;
+struct Key;
+template<typename T> class memoryview;
 
 enum class MenuStyle
 {
diff --git a/src/value.hh b/src/value.hh
index bf051353..86bbfea2 100644
--- a/src/value.hh
+++ b/src/value.hh
@@ -67,7 +67,7 @@ private:
 
 struct ValueId : public StronglyTypedNumber<ValueId, int>
 {
-    constexpr ValueId(int value = 0) : StronglyTypedNumber<ValueId>(value) {}
+    constexpr ValueId(int value = 0) : StronglyTypedNumber(value) {}
 
     static ValueId get_free_id()
     {
diff --git a/src/window.hh b/src/window.hh
index e2bb91b1..c5efdf27 100644
--- a/src/window.hh
+++ b/src/window.hh
@@ -1,10 +1,9 @@
 #ifndef window_hh_INCLUDED
 #define window_hh_INCLUDED
 
-#include "completion.hh"
 #include "display_buffer.hh"
 #include "highlighter_group.hh"
-#include "selection.hh"
+#include "option_manager.hh"
 #include "safe_ptr.hh"
 #include "scope.hh"