diff --git a/ChangeLog b/ChangeLog
index f1951596d5..23ed0e91af 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu May 21 12:07:43 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* include/ruby/ruby.h (RB_EVENT_HOOKS_HAVE_CALLBACK_DATA):
+	  new macro for compatibility check.
+
 Thu May 21 01:43:40 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* include/ruby/ruby.h (rb_long2int, RARRAY_LENINT): check long to
diff --git a/README.EXT b/README.EXT
index 7836545bbe..c28c259738 100644
--- a/README.EXT
+++ b/README.EXT
@@ -1234,7 +1234,7 @@ Specifies the name of the script ($0).
 
 ** Hooks for the Interpreter Events
 
- void rb_add_event_hook(rb_event_hook_func_t func, rb_event_t events)
+ void rb_add_event_hook(rb_event_hook_func_t func, rb_event_flag_t events, VALUE data)
 
 Adds a hook function for the specified interpreter events.
 events should be Or'ed value of:
@@ -1251,9 +1251,13 @@ events should be Or'ed value of:
 
 The definition of rb_event_hook_func_t is below:
 
- typedef void (*rb_event_hook_func_t)(rb_event_t event, NODE *node,
+ typedef void (*rb_event_hook_func_t)(rb_event_t event, VALUE data,
  				      VALUE self, ID id, VALUE klass)
 
+The third argument `data' to rb_add_event_hook() is passed to the hook
+function as the second argument, which was the pointer to the current
+NODE in 1.8.  See RB_EVENT_HOOKS_HAVE_CALLBACK_DATA below.
+
  int rb_remove_event_hook(rb_event_hook_func_t func)
 
 Removes the specified hook function.
@@ -1293,6 +1297,11 @@ Defined in ruby.h and means correspoinding header is available.  For
 instance, when HAVE_RUBY_ST_H is defined you should use ruby/st.h not
 mere st.h.
 
+ RB_EVENT_HOOKS_HAVE_CALLBACK_DATA
+
+Means that rb_add_event_hook() takes the third argument `data', to be
+passed to the given event hook function.
+
 Appendix C. Functions Available in extconf.rb
 
 These functions are available in extconf.rb:
diff --git a/README.EXT.ja b/README.EXT.ja
index 14192461b7..a07fddf09e 100644
--- a/README.EXT.ja
+++ b/README.EXT.ja
@@ -1332,7 +1332,7 @@ void ruby_script(char *name)
 
 ** インタプリタのイベントのフック
 
- void rb_add_event_hook(rb_event_hook_func_t func, rb_event_t events)
+ void rb_add_event_hook(rb_event_hook_func_t func, rb_event_flag_t events, VALUE data)
 
 指定されたインタプリタのイベントに対するフック関数を追加します．
 eventsは以下の値のorでなければなりません:
@@ -1349,9 +1349,13 @@ events
 
 rb_event_hook_func_tの定義は以下の通りです:
 
- typedef void (*rb_event_hook_func_t)(rb_event_t event, NODE *node,
+ typedef void (*rb_event_hook_func_t)(rb_event_t event, VALUE data,
  				      VALUE self, ID id, VALUE klass)
 
+rb_add_event_hook() の第3引数 data は，フック関数の第2引数と
+して渡されます．これは1.8では現在のNODEへのポインタでした．以
+下の RB_EVENT_HOOKS_HAVE_CALLBACK_DATA も参照してください．
+
  int rb_remove_event_hook(rb_event_hook_func_t func)
 
 指定されたフック関数を削除します．
@@ -1393,6 +1397,10 @@ HAVE_RUBY_*_H
   を意味する．たとえば，HAVE_RUBY_ST_H が定義されている場合は
   単なる st.h ではなく ruby/st.h を使用する．
 
+RB_EVENT_HOOKS_HAVE_CALLBACK_DATA
+
+  rb_add_event_hook() がフック関数に渡す data を第3引数として
+  受け取ることを意味する．
 
 Appendix C. extconf.rbで使える関数たち
 
diff --git a/include/ruby/ruby.h b/include/ruby/ruby.h
index 440bfe2ed1..8e8486b105 100644
--- a/include/ruby/ruby.h
+++ b/include/ruby/ruby.h
@@ -1220,6 +1220,7 @@ typedef struct rb_event_hook_struct {
     struct rb_event_hook_struct *next;
 } rb_event_hook_t;
 
+#define RB_EVENT_HOOKS_HAVE_CALLBACK_DATA 1
 void rb_add_event_hook(rb_event_hook_func_t func, rb_event_flag_t events,
 		       VALUE data);
 int rb_remove_event_hook(rb_event_hook_func_t func);