diff --git a/lib/http/cookie.rb b/lib/http/cookie.rb
index 8be45be..6aeffed 100644
--- a/lib/http/cookie.rb
+++ b/lib/http/cookie.rb
@@ -361,15 +361,28 @@ class HTTP::Cookie
 
   # See #domain.
   def domain=(domain)
-    if DomainName === domain
+    case domain
+    when nil
+      @for_domain = false
+      if @origin
+        @domain_name = DomainName.new(@origin.host)
+        @domain = @domain_name.hostname
+      else
+        @domain_name = @domain = nil
+      end
+      return nil
+    when DomainName
       @domain_name = domain
     else
       domain = check_string_type(domain) or
         raise TypeError, "#{domain.class} is not a String"
       if domain.start_with?('.')
-        @for_domain = true
+        for_domain = true
         domain = domain[1..-1]
       end
+      if domain.empty?
+        return self.domain = nil
+      end
       # Do we really need to support this?
       if domain.match(/\A([^:]+):[0-9]+\z/)
         domain = $1
@@ -377,8 +390,10 @@ class HTTP::Cookie
       @domain_name = DomainName.new(domain)
     end
     # RFC 6265 5.3 5.
-    if @domain_name.domain.nil? # a public suffix or IP address
+    if domain_name.domain.nil? # a public suffix or IP address
       @for_domain = false
+    else
+      @for_domain = for_domain unless for_domain.nil?
     end
     @domain = @domain_name.hostname
   end
diff --git a/test/test_http_cookie.rb b/test/test_http_cookie.rb
index 0f86837..ad4ab1f 100644
--- a/test/test_http_cookie.rb
+++ b/test/test_http_cookie.rb
@@ -610,7 +610,7 @@ class TestHTTPCookie < Test::Unit::TestCase
       HTTP::Cookie.new(cookie_values(:value => 'bar')))
   end
 
-  def test_new_rejects_cookies_that_do_not_contain_an_embedded_dot
+  def test_new_tld_domain
     url = URI 'http://rubyforge.org/'
 
     tld_cookie1 = HTTP::Cookie.new(cookie_values(:domain => 'org', :origin => url))
@@ -707,6 +707,24 @@ class TestHTTPCookie < Test::Unit::TestCase
       end
     }
     assert 'example.com', cookie.domain
+
+    url = URI 'http://rubyforge.org/'
+
+    [nil, '', '.'].each { |d|
+      cookie = HTTP::Cookie.new('Foo', 'Bar', :path => '/')
+      cookie.domain = d
+      assert_equal nil, cookie.domain, "domain=#{d.inspect}"
+      assert_equal nil, cookie.domain_name, "domain=#{d.inspect}"
+      assert_raises(ArgumentError) {
+        cookie.acceptable?
+      }
+
+      cookie = HTTP::Cookie.new('Foo', 'Bar', :path => '/')
+      cookie.origin = url
+      cookie.domain = d
+      assert_equal url.host, cookie.domain, "domain=#{d.inspect}"
+      assert_equal true, cookie.acceptable?, "domain=#{d.inspect}"
+    }
   end
 
   def test_origin=