diff --git a/ChangeLog b/ChangeLog
index 6335008012..b7e2c33dcb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Thu Jun 20 13:14:06 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* error.c (rb_check_backtrace): evaluate RARRAY_AREF only once.
+	  the first argument of RB_TYPE_P is expanded twice for non-immediate
+	  types.
+
 Thu Jun 20 08:09:29 2013  Koichi Sasada  <ko1@atdot.net>
 
 	* tool/gcbench.rb: Summary in one line.
diff --git a/error.c b/error.c
index e65e04fc10..eac254ca44 100644
--- a/error.c
+++ b/error.c
@@ -721,7 +721,8 @@ rb_check_backtrace(VALUE bt)
 	    rb_raise(rb_eTypeError, err);
 	}
 	for (i=0;i<RARRAY_LEN(bt);i++) {
-	    if (!RB_TYPE_P(RARRAY_AREF(bt, i), T_STRING)) {
+	    VALUE e = RARRAY_AREF(bt, i);
+	    if (!RB_TYPE_P(e, T_STRING)) {
 		rb_raise(rb_eTypeError, err);
 	    }
 	}