diff --git a/ChangeLog b/ChangeLog
index f0ef6cf246..f459b2f37c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Sun Jan 31 23:20:43 2010  wanabe  <s.wanabe@gmail.com>
+
+	* io.c (rb_io_each_codepoint): use cbuf when needs readconv.
+
 Sun Jan 31 23:07:23 2010  Yusuke Endoh  <mame@tsg.ne.jp>
 
 	* test/ruby/test_dir.rb: use string instead of symbol as file name.
diff --git a/io.c b/io.c
index e69fc9dc46..4017778e0c 100644
--- a/io.c
+++ b/io.c
@@ -2860,8 +2860,8 @@ rb_io_each_codepoint(VALUE io)
 	    c = rb_enc_codepoint(fptr->cbuf+fptr->cbuf_off,
 				 fptr->cbuf+fptr->cbuf_off+fptr->cbuf_len,
 				 fptr->encs.enc);
-	    fptr->rbuf_off += n;
-	    fptr->rbuf_len -= n;
+	    fptr->cbuf_off += n;
+	    fptr->cbuf_len -= n;
 	    rb_yield(UINT2NUM(c));
 	}
     }