diff --git a/ChangeLog b/ChangeLog
index a0b4bae4d1..fbe2ded9ee 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,9 @@
+Mon Jan 11 16:52:05 2010  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* string.c (rb_str_strlen): added. [ruby-dev:40028]
+
+	* include/ruby/intern.h (rb_str_strlen): declared.
+
 Mon Jan 11 13:30:35 2010  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* lib/webrick/accesslog.rb (WEBrick::AccessLog#format): fixed typo.
diff --git a/include/ruby/intern.h b/include/ruby/intern.h
index 14e23b857d..116afa520b 100644
--- a/include/ruby/intern.h
+++ b/include/ruby/intern.h
@@ -662,6 +662,7 @@ VALUE rb_str_associated(VALUE);
 void rb_str_setter(VALUE, ID, VALUE*);
 VALUE rb_str_intern(VALUE);
 VALUE rb_sym_to_s(VALUE);
+long rb_str_strlen(VALUE);
 VALUE rb_str_length(VALUE);
 long rb_str_offset(VALUE, long);
 size_t rb_str_capacity(VALUE);
diff --git a/string.c b/string.c
index 2dcc3305af..78620b8048 100644
--- a/string.c
+++ b/string.c
@@ -1079,6 +1079,12 @@ str_strlen(VALUE str, rb_encoding *enc)
     return n;
 }
 
+long
+rb_str_strlen(VALUE str)
+{
+    return str_strlen(str, STR_ENC_GET(str));
+}
+
 /*
  *  call-seq:
  *     str.length   => integer