diff --git a/actionpack/CHANGELOG b/actionpack/CHANGELOG
index 9eab6835870712445100662c1ee0668fa86b8406..0d679f93e2416d47fa2623d29763aa5c97daa4af 100644
--- a/actionpack/CHANGELOG
+++ b/actionpack/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* request.host works with IPv6 addresses.  #9458 [yuya]
+
 * Fix bug where action caching sets the content type to the ActionCachePath object.  Closes #9282 [mindforge]
 
 * Find layouts even if they're not in the first view_paths directory.  Closes #9258 [caio]
diff --git a/actionpack/lib/action_controller/cgi_process.rb b/actionpack/lib/action_controller/cgi_process.rb
index fa7afd419720ed3fc8cdb962bdfb815ca278cae5..6e8098e746eadc386de2d3a02a1133b977f5b41d 100644
--- a/actionpack/lib/action_controller/cgi_process.rb
+++ b/actionpack/lib/action_controller/cgi_process.rb
@@ -92,7 +92,7 @@ def host_with_port
     end
 
     def host
-      host_with_port[/^[^:]+/]
+      host_with_port.sub(/:\d+$/, '')
     end
 
     def port
diff --git a/actionpack/test/controller/cgi_test.rb b/actionpack/test/controller/cgi_test.rb
index a5b24ebcd4ed39abb659c8133410c732620f26d7..fe94d7c7a6a05f90045ee66a22ad42b9439d0db7 100755
--- a/actionpack/test/controller/cgi_test.rb
+++ b/actionpack/test/controller/cgi_test.rb
@@ -47,6 +47,18 @@ def test_host_with_port_falls_back_to_server_addr_if_necessary
     assert_equal "207.7.108.53:8007", @request.host_with_port
   end
 
+  def test_host_if_ipv6_reference
+    @request_hash.delete "HTTP_X_FORWARDED_HOST"
+    @request_hash['HTTP_HOST'] = "[2001:1234:5678:9abc:def0::dead:beef]"
+    assert_equal "[2001:1234:5678:9abc:def0::dead:beef]", @request.host
+  end
+
+  def test_host_if_ipv6_reference_with_port
+    @request_hash.delete "HTTP_X_FORWARDED_HOST"
+    @request_hash['HTTP_HOST'] = "[2001:1234:5678:9abc:def0::dead:beef]:8008"
+    assert_equal "[2001:1234:5678:9abc:def0::dead:beef]", @request.host
+  end
+
   def test_cookie_syntax_resilience
     cookies = CGI::Cookie::parse(@request_hash["HTTP_COOKIE"]);
     assert_equal ["c84ace84796670c052c6ceb2451fb0f2"], cookies["_session_id"]