diff --git a/ChangeLog b/ChangeLog
index 652f0a730a..68e5699d82 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Wed Feb  2 20:25:04 2011  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* include/ruby/encoding.h (rb_enc_step_back): cast 4th argument 'n'
+	  as int because Ruby usually treats length value as long but
+	  onigenc_step_back's 4th argument is int.
+
 Thu Feb  3 07:20:46 2011  Aaron Patterson <aaron@tenderlovemaking.com>
 
 	* ext/psych/lib/psych/visitors/to_ruby.rb: use Regexp::NOENCODING
diff --git a/include/ruby/encoding.h b/include/ruby/encoding.h
index 94953c0906..bb86e86aac 100644
--- a/include/ruby/encoding.h
+++ b/include/ruby/encoding.h
@@ -162,7 +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))
+#define rb_enc_step_back(s,p,e,n,enc) (char *)onigenc_step_back(enc,(UChar*)(s),(UChar*)(p),(UChar*)(e),(int)(n))
 
 /* ptr, ptr, encoding -> newline_or_not */
 #define rb_enc_is_newline(p,end,enc)  ONIGENC_IS_MBC_NEWLINE(enc,(UChar*)(p),(UChar*)(end))