diff --git a/ChangeLog b/ChangeLog
index 6637f0c01c..1bf49ce281 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Thu Oct 10 23:01:16 2013  Masaki Matsushita  <glass.saga@gmail.com>
+
+	* array.c (rb_ary_or): use rb_hash_keys().
+
 Thu Oct 10 21:36:16 2013  Masaki Matsushita  <glass.saga@gmail.com>
 
 	* array.c (rb_ary_compact_bang): use ary_resize_smaller().
diff --git a/array.c b/array.c
index c45c992840..fc2672bda8 100644
--- a/array.c
+++ b/array.c
@@ -4004,21 +4004,8 @@ rb_ary_or(VALUE ary1, VALUE ary2)
     long i;
 
     ary2 = to_ary(ary2);
-    ary3 = rb_ary_new2(RARRAY_LEN(ary1)+RARRAY_LEN(ary2));
     hash = ary_add_hash(ary_make_hash(ary1), ary2);
-
-    for (i=0; i<RARRAY_LEN(ary1); i++) {
-	vv = (st_data_t)(v = rb_ary_elt(ary1, i));
-	if (st_delete(rb_hash_tbl_raw(hash), &vv, 0)) {
-	    rb_ary_push(ary3, v);
-	}
-    }
-    for (i=0; i<RARRAY_LEN(ary2); i++) {
-	vv = (st_data_t)(v = rb_ary_elt(ary2, i));
-	if (st_delete(rb_hash_tbl_raw(hash), &vv, 0)) {
-	    rb_ary_push(ary3, v);
-	}
-    }
+    ary3 = rb_hash_keys(hash);
     ary_recycle_hash(hash);
     return ary3;
 }