diff --git a/ChangeLog b/ChangeLog
index c3a606d9bd..49c3790e0f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Thu Mar 19 04:46:36 2015  Koichi Sasada  <ko1@atdot.net>
+
+	* enum.c (enum_sort_by): add WBs.
+
 Thu Mar 19 03:37:52 2015  Koichi Sasada  <ko1@atdot.net>
 
 	* gc.c (check_rvalue_consistency): refactoring.
diff --git a/enum.c b/enum.c
index cd4366281f..f561960dd6 100644
--- a/enum.c
+++ b/enum.c
@@ -846,8 +846,8 @@ enum_sort(VALUE obj)
 
 #define SORT_BY_BUFSIZE 16
 struct sort_by_data {
-    VALUE ary;
-    VALUE buf;
+    const VALUE ary;
+    const VALUE buf;
     long n;
 };
 
@@ -989,8 +989,8 @@ enum_sort_by(VALUE obj)
     memo = MEMO_NEW(0, 0, 0);
     OBJ_INFECT(memo, obj);
     data = (struct sort_by_data *)&memo->v1;
-    data->ary = ary;
-    data->buf = buf;
+    RB_OBJ_WRITE(memo, &data->ary, ary);
+    RB_OBJ_WRITE(memo, &data->buf, buf);
     data->n = 0;
     rb_block_call(obj, id_each, 0, 0, sort_by_i, (VALUE)memo);
     ary = data->ary;