diff --git a/ChangeLog b/ChangeLog
index 5c053c5754..2967c6c88c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Jan 10 10:15:03 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* io.c (io_encoding_set): IO.pipe("euc-jp", nil) should work as
+	  IO.pipe("euc-jp", nil).  [ruby-dev:33000]
+
 Thu Jan 10 02:41:22 2008  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* io.c (rb_io_binmode): should not alter encoding.  [ruby-dev:32918]
diff --git a/io.c b/io.c
index 75b7b4f34d..2fc199d861 100644
--- a/io.c
+++ b/io.c
@@ -5621,6 +5621,7 @@ io_new_instance(VALUE args)
 static void
 io_encoding_set(rb_io_t *fptr, int argc, VALUE v1, VALUE v2)
 {
+    if (NIL_P(v2)) argc = 1;
     if (argc == 2) {
 	fptr->enc2 = rb_to_encoding(v1);
 	fptr->enc = rb_to_encoding(v2);