diff --git a/lib/http/cookie.rb b/lib/http/cookie.rb
index 6f30477..c76524f 100644
--- a/lib/http/cookie.rb
+++ b/lib/http/cookie.rb
@@ -9,6 +9,9 @@ end
 
 # This class is used to represent an HTTP Cookie.
 class HTTP::Cookie
+  # Maximum number of bytes per cookie (RFC 6265 6.1 requires 4096 at least)
+  MAX_LENGTH = 4096
+
   PERSISTENT_PROPERTIES = %w[
     name        value
     domain      for_domain  path
@@ -153,6 +156,11 @@ class HTTP::Cookie
 
       [].tap { |cookies|
         set_cookie.split(/,(?=[^;,]*=)|,$/).each { |c|
+          if c.bytesize > MAX_LENGTH
+            logger.warn("Cookie definition too long: #{c}") if logger
+            next
+          end
+
           cookie_elem = c.split(/;+/)
           first_elem = cookie_elem.shift
           first_elem.strip!
diff --git a/test/test_http_cookie.rb b/test/test_http_cookie.rb
index e1f7d18..bf9edba 100644
--- a/test/test_http_cookie.rb
+++ b/test/test_http_cookie.rb
@@ -1,3 +1,4 @@
+# -*- coding: utf-8 -*-
 require File.expand_path('helper', File.dirname(__FILE__))
 
 class TestHTTPCookie < Test::Unit::TestCase
@@ -79,6 +80,19 @@ class TestHTTPCookie < Test::Unit::TestCase
     end
   end
 
+  def test_parse_too_long_cookie
+    uri = URI.parse 'http://example'
+
+    cookie_str = "foo=#{'クッキー' * 340}; path=/ab/"
+    assert_equal(HTTP::Cookie::MAX_LENGTH - 1, cookie_str.bytesize)
+
+    assert_equal 1, HTTP::Cookie.parse(cookie_str, :origin => uri).size
+
+    assert_equal 1, HTTP::Cookie.parse(cookie_str.sub(';', 'x;'), :origin => uri).size
+
+    assert_equal 0, HTTP::Cookie.parse(cookie_str.sub(';', 'xx;'), :origin => uri).size
+  end
+
   def test_parse_quoted
     cookie_str =
       "quoted=\"value\"; Expires=Sun, 06 Nov 2011 00:11:18 GMT; Path=/"