diff --git a/ChangeLog b/ChangeLog
index da3cfb3310..28dfd653fb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Mon May 30 22:02:01 2016  Kazuki Yamaguchi  <k@rhe.jp>
+
+	* ext/openssl/ossl_asn1.c (time_to_time_t): Use NUM2TIMET() instead of
+	  NUM2LONG(). time_t may be larger than long.
+	  [ruby-core:45552] [Bug #6571]
+
 Mon May 30 21:15:37 2016  Martin Duerst  <duerst@it.aoyama.ac.jp>
 
 	* string.c: Document current behavior for other case mapping methods
diff --git a/ext/openssl/ossl_asn1.c b/ext/openssl/ossl_asn1.c
index e77adbf9f8..43a3d2d88a 100644
--- a/ext/openssl/ossl_asn1.c
+++ b/ext/openssl/ossl_asn1.c
@@ -75,15 +75,10 @@ asn1time_to_time(ASN1_TIME *time)
     return rb_funcall2(rb_cTime, rb_intern("utc"), 6, argv);
 }
 
-/*
- * This function is not exported in Ruby's *.h
- */
-extern struct timeval rb_time_timeval(VALUE);
-
 time_t
 time_to_time_t(VALUE time)
 {
-    return (time_t)NUM2LONG(rb_Integer(time));
+    return (time_t)NUM2TIMET(rb_Integer(time));
 }
 
 /*