diff --git a/ChangeLog b/ChangeLog
index f3aa773c95..2994d819d5 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Aug  4 07:14:49 2013  Tanaka Akira  <akr@fsij.org>
+
+	* README.EXT, README.EXT.ja: Mention rb_integer_pack and
+	  rb_integer_unpack.
+
 Sun Aug  4 01:54:45 2013  Tanaka Akira  <akr@fsij.org>
 
 	* bignum.c (BARY_TRUNC): New macro.
diff --git a/README.EXT b/README.EXT
index 6f40185047..dc3136c414 100644
--- a/README.EXT
+++ b/README.EXT
@@ -1060,6 +1060,10 @@ NUM2SSIZET(value), SSIZET2NUM(ssize) ::
 
   Numeric <-> ssize_t
 
+rb_integer_pack(value, words, numwords, wordsize, nails, flags), rb_integer_unpack(words, numwords, wordsize, nails, flags) ::
+
+  Numeric <-> Arbitrary size integer buffer
+
 NUM2DBL(value) ::
 
   Numeric -> double
diff --git a/README.EXT.ja b/README.EXT.ja
index 14c35f3707..cd7fda5a4f 100644
--- a/README.EXT.ja
+++ b/README.EXT.ja
@@ -1108,6 +1108,7 @@ Data_Get_Struct(data, type, sval) ::
   NUM2OFFT(value), OFFT2NUM(off)
   NUM2SIZET(value), SIZET2NUM(size)
   NUM2SSIZET(value), SSIZET2NUM(ssize)
+  rb_integer_pack(value, words, numwords, wordsize, nails, flags), rb_integer_unpack(words, numwords, wordsize, nails, flags)
   NUM2DBL(value)
   rb_float_new(f)
   StringValue(value)