diff --git a/ChangeLog b/ChangeLog
index 1718115510..9ee92d56f0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -2,6 +2,11 @@ Fri Dec 21 12:55:39 2007  Tanaka Akira  <akr@fsij.org>
 
 	* lib/runit, lib/rubyunit.rb, test/testunit/runit: removed.
 
+Fri Dec 21 12:45:49 2007  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* string.c (rb_str_chomp_bang): avoid unnecessary loop using
+	  rb_enc_prev_char().
+
 Fri Dec 21 12:32:08 2007  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* file.c (Init_File): File.exists? revived.
diff --git a/string.c b/string.c
index 6e998ee17a..4079a8cf4f 100644
--- a/string.c
+++ b/string.c
@@ -4538,12 +4538,8 @@ rb_str_chomp_bang(int argc, VALUE *argv, VALUE str)
     if (p[len-1] == newline &&
 	(rslen <= 1 ||
 	 memcmp(RSTRING_PTR(rs), pp, rslen) == 0)) {
-	if (rb_enc_mbmaxlen(enc) > 1) {
-	    while (p < pp) {
-		p += rb_enc_mbclen(p, e, enc);
-	    }
-	    if (p != pp) return Qnil;
-	}
+	if (ONIGENC_LEFT_ADJUST_CHAR_HEAD(enc,p,pp) != (const UChar*)pp)
+	    return Qnil;
 	rb_str_modify(str);
 	STR_SET_LEN(str, RSTRING_LEN(str) - rslen);
 	RSTRING_PTR(str)[RSTRING_LEN(str)] = '\0';