diff --git a/ChangeLog b/ChangeLog
index 4f749a9439..abff4b1a07 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat May 31 15:17:36 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* include/ruby/mvm.h: new header file for MVM, and moved rb_vm_t and
+	  rb_thread_t from vm_core.h.
+
 Sat May 31 12:02:23 2008  Tanaka Akira  <akr@fsij.org>
 
 	* test/ruby/envutil.rb (assert_normal_exit): show pid when fail.
diff --git a/include/ruby.h b/include/ruby.h
index b1fb46c897..cbe5aaa3bf 100644
--- a/include/ruby.h
+++ b/include/ruby.h
@@ -1 +1,21 @@
+/**********************************************************************
+
+  ruby/mvm.h -
+
+  $Author$
+  created at: Sun 10 12:06:15 Jun JST 2007
+
+  Copyright (C) 2007-2008 Yukihiro Matsumoto
+
+**********************************************************************/
+
+#ifndef RUBY_H
+#define RUBY_H 1
+
 #include <ruby/ruby.h>
+#if RUBY_VM
+#include <ruby/mvm.h>
+#endif
+
+extern void ruby_set_debug_option(const char *);
+#endif /* RUBY_H */
diff --git a/include/ruby/mvm.h b/include/ruby/mvm.h
new file mode 100644
index 0000000000..6b6a2f5232
--- /dev/null
+++ b/include/ruby/mvm.h
@@ -0,0 +1,18 @@
+/**********************************************************************
+
+  ruby/mvm.h -
+
+  $Author$
+  created at: Sat May 31 15:17:36 2008
+
+  Copyright (C) 2008 Yukihiro Matsumoto
+
+**********************************************************************/
+
+#ifndef RUBY_MVM_H
+#define RUBY_MVM_H 1
+
+typedef struct rb_vm_struct rb_vm_t;
+typedef struct rb_thread_struct rb_thread_t;
+
+#endif /* RUBY_MVM_H */
diff --git a/main.c b/main.c
index 455c181d16..c2120d257c 100644
--- a/main.c
+++ b/main.c
@@ -10,7 +10,7 @@
 **********************************************************************/
 
 #undef RUBY_EXPORT
-#include "ruby/ruby.h"
+#include "ruby.h"
 #ifdef HAVE_LOCALE_H
 #include <locale.h>
 #endif
@@ -21,7 +21,6 @@ int
 main(int argc, char **argv, char **envp)
 {
 #ifdef RUBY_DEBUG_ENV
-    extern void ruby_set_debug_option(const char *);
     ruby_set_debug_option(getenv("RUBY_DEBUG"));
 #endif
 #ifdef HAVE_LOCALE_H
diff --git a/vm_core.h b/vm_core.h
index f0fdafef2d..08c6449c78 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -17,6 +17,7 @@
 #include <setjmp.h>
 
 #include "ruby/ruby.h"
+#include "ruby/mvm.h"
 #include "ruby/signal.h"
 #include "ruby/st.h"
 #include "ruby/node.h"
@@ -285,7 +286,8 @@ typedef struct rb_iseq_struct rb_iseq_t;
 #define GetVMPtr(obj, ptr) \
   GetCoreDataFromValue(obj, rb_vm_t, ptr)
 
-typedef struct rb_vm_struct {
+struct rb_vm_struct
+{
     VALUE self;
 
     rb_thread_lock_t global_interpreter_lock;
@@ -320,7 +322,7 @@ typedef struct rb_vm_struct {
 #if defined(ENABLE_VM_OBJSPACE) && ENABLE_VM_OBJSPACE
     struct rb_objspace *objspace;
 #endif
-} rb_vm_t;
+};
 
 typedef struct {
     VALUE *pc;			/* cfp[0] */
@@ -378,8 +380,6 @@ struct rb_unblock_callback {
     void *arg;
 };
 
-typedef struct rb_thread_struct rb_thread_t;
-
 struct rb_thread_struct
 {
     VALUE self;