diff --git a/ChangeLog b/ChangeLog
index a20eb74a86..38192bf8d5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sat Feb  5 02:08:37 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* vm.c (ruby_thread_data_type): add prefix.
+
 Sat Feb  5 00:59:54 2011  KOSAKI Motohiro  <kosaki.motohiro@gmail.com>
 
 	* vm_core.h (GetThreadPtr): use TypedData_Get_Struct() instead
diff --git a/vm.c b/vm.c
index 1dbf2ecabb..d0c25929f0 100644
--- a/vm.c
+++ b/vm.c
@@ -1756,7 +1756,8 @@ thread_memsize(const void *ptr)
     }
 }
 
-const rb_data_type_t thread_data_type = {
+#define thread_data_type ruby_thread_data_type
+const rb_data_type_t ruby_thread_data_type = {
     "VM/thread",
     {
 	rb_thread_mark,
diff --git a/vm_core.h b/vm_core.h
index f20dfb02f3..997ed38f13 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -347,10 +347,10 @@ typedef struct rb_block_struct {
     VALUE proc;
 } rb_block_t;
 
-extern const rb_data_type_t thread_data_type;
+extern const rb_data_type_t ruby_thread_data_type;
 
 #define GetThreadPtr(obj, ptr) \
-    TypedData_Get_Struct((obj), rb_thread_t, &thread_data_type, (ptr))
+    TypedData_Get_Struct((obj), rb_thread_t, &ruby_thread_data_type, (ptr))
 
 enum rb_thread_status {
     THREAD_TO_KILL,