diff --git a/ChangeLog b/ChangeLog
index d18e0c0d9b..4b1168320f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Dec 15 23:16:13 2011  CHIKANAGA Tomoyuki  <nagachika00@gmail.com>
+
+	* error.c (builtin_type_name): don't return pointer to the buffer of
+	  temporary String object.
+
 Thu Dec 15 17:56:58 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* io.c (argf_type): make typed data.
diff --git a/error.c b/error.c
index e3348dc7b5..6844f992a6 100644
--- a/error.c
+++ b/error.c
@@ -392,9 +392,11 @@ builtin_type_name(VALUE x)
     else if (SYMBOL_P(x)) {
 	etype = "Symbol";
     }
-    else if (rb_special_const_p(x)) {
-	x = rb_obj_as_string(x);
-	etype = StringValuePtr(x);
+    else if (RB_TYPE_P(x, T_TRUE)) {
+	etype = "true";
+    }
+    else if (RB_TYPE_P(x, T_FALSE)) {
+	etype = "false";
     }
     else {
 	etype = rb_obj_classname(x);