diff --git a/ChangeLog b/ChangeLog
index 491b182da3..25d3ab3fef 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,7 @@
-Thu Mar 24 12:43:05 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+Thu Mar 24 12:43:26 2016  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* ext/date/date_core.c (dt_lite_iso8601): strftimev() always
+	  returns a String, so append them directly.
 
 	* ext/date/date_core.c (d_lite_jisx0301, iso8601_timediv),
 	  (dt_lite_jisx0301): format by the format string in local buffer
diff --git a/ext/date/date_core.c b/ext/date/date_core.c
index dbe8cb97da..a863f9c17c 100644
--- a/ext/date/date_core.c
+++ b/ext/date/date_core.c
@@ -8350,8 +8350,8 @@ dt_lite_iso8601(int argc, VALUE *argv, VALUE self)
     if (argc >= 1)
 	n = NUM2LONG(argv[0]);
 
-    return f_add(strftimev("%Y-%m-%d", self, set_tmx),
-		 iso8601_timediv(self, n));
+    return rb_str_append(strftimev("%Y-%m-%d", self, set_tmx),
+			 iso8601_timediv(self, n));
 }
 
 /*