diff --git a/ChangeLog b/ChangeLog
index 285dbd15ce..17c0a285a2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Aug  8 19:56:52 2013  Koichi Sasada  <ko1@atdot.net>
+
+	* string.c (rb_str_format_m): use RARRAY_RAWPTR() instead of
+	  RARRAY_PTR() because there is no new reference.
+
 Thu Aug  8 19:55:51 2013  Koichi Sasada  <ko1@atdot.net>
 
 	* include/ruby/ruby.h: define USE_RGENGC_LOGGING_WB_UNPROTECT.
diff --git a/string.c b/string.c
index 81a368f4e5..2d328e45d5 100644
--- a/string.c
+++ b/string.c
@@ -1309,7 +1309,7 @@ rb_str_format_m(VALUE str, VALUE arg)
     volatile VALUE tmp = rb_check_array_type(arg);
 
     if (!NIL_P(tmp)) {
-	return rb_str_format(RARRAY_LENINT(tmp), RARRAY_PTR(tmp), str);
+	return rb_str_format(RARRAY_LENINT(tmp), RARRAY_RAWPTR(tmp), str);
     }
     return rb_str_format(1, &arg, str);
 }