diff --git a/ChangeLog b/ChangeLog
index acadee538d..b756b13648 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Jan 30 12:56:13 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* include/ruby/encoding.h (rb_enc_step_back): new function to step
+	  back n characters.
+
 Sun Jan 30 12:53:38 2011  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* enc/emacs_mule.c (emacsmule_islead): fix inverse condition.
diff --git a/include/ruby/encoding.h b/include/ruby/encoding.h
index efc99aa0af..94953c0906 100644
--- a/include/ruby/encoding.h
+++ b/include/ruby/encoding.h
@@ -162,6 +162,7 @@ int rb_enc_codelen(int code, rb_encoding *enc);
 /* start, ptr, end, encoding -> next_char */
 #define rb_enc_left_char_head(s,p,e,enc) (char *)onigenc_get_left_adjust_char_head(enc,(UChar*)(s),(UChar*)(p),(UChar*)(e))
 #define rb_enc_right_char_head(s,p,e,enc) (char *)onigenc_get_right_adjust_char_head(enc,(UChar*)(s),(UChar*)(p),(UChar*)(e))
+#define rb_enc_step_back(s,p,e,n,enc) (char *)onigenc_step_back(enc,(UChar*)(s),(UChar*)(p),(UChar*)(e),(n))
 
 /* ptr, ptr, encoding -> newline_or_not */
 #define rb_enc_is_newline(p,end,enc)  ONIGENC_IS_MBC_NEWLINE(enc,(UChar*)(p),(UChar*)(end))