diff --git a/actionpack/lib/action_controller/session/cookie_store.rb b/actionpack/lib/action_controller/session/cookie_store.rb
index 0a2a91f01e..5e5ef1bfb0 100644
--- a/actionpack/lib/action_controller/session/cookie_store.rb
+++ b/actionpack/lib/action_controller/session/cookie_store.rb
@@ -117,7 +117,7 @@ class CGI::Session::CookieStore
   def delete
     @data = nil
     clear_old_cookie_value
-    write_cookie('value' => '', 'expires' => 1.year.ago)
+    write_cookie('value' => nil, 'expires' => 1.year.ago)
   end
 
   # Generate the HMAC keyed message digest. Uses SHA1 by default.
diff --git a/actionpack/test/controller/session/cookie_store_test.rb b/actionpack/test/controller/session/cookie_store_test.rb
index 0fdfa29568..d308f2a31b 100755
--- a/actionpack/test/controller/session/cookie_store_test.rb
+++ b/actionpack/test/controller/session/cookie_store_test.rb
@@ -175,7 +175,7 @@ class CookieStoreTest < Test::Unit::TestCase
     def assert_cookie_deleted(session, message = 'Expected session deletion cookie to be set')
       assert_equal 1, session.cgi.output_cookies.size
       cookie = session.cgi.output_cookies.first
-      assert_cookie cookie, nil, 1.year.ago.to_date, message
+      assert_cookie cookie, nil, 1.year.ago.to_date, "#{message}: #{cookie.name} => #{cookie.value}"
     end
 
     def assert_cookie(cookie, value = nil, expires = nil, message = nil)