diff --git a/ChangeLog b/ChangeLog
index 0d27505070..4d5f4e0d58 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Jan 14 14:56:57 2011  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* lib/net/imap.rb: use bytesize for binary strings.
+	  patched by Yoshimasa Niwa. [ruby-core:34222]
+
 Fri Jan 14 14:01:12 2011  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* pack.c (pack_unpack): the resulted string of unpack('M') must have
diff --git a/lib/net/imap.rb b/lib/net/imap.rb
index dd0d6b42b7..0b76a9ff4a 100644
--- a/lib/net/imap.rb
+++ b/lib/net/imap.rb
@@ -1269,7 +1269,7 @@ module Net
     end
 
     def send_literal(str)
-      put_string("{" + str.length.to_s + "}" + CRLF)
+      put_string("{" + str.bytesize.to_s + "}" + CRLF)
       @continuation_request_arrival.wait
       raise @exception if @exception
       put_string(str)
@@ -2603,7 +2603,7 @@ module Net
           return '""'
         when /[\x80-\xff\r\n]/n
           # literal
-          return "{" + str.length.to_s + "}" + CRLF + str
+          return "{" + str.bytesize.to_s + "}" + CRLF + str
         when /[(){ \x00-\x1f\x7f%*"\\]/n
           # quoted string
           return '"' + str.gsub(/["\\]/n, "\\\\\\&") + '"'