diff --git a/actionpack/lib/action_controller/session/cookie_store.rb b/actionpack/lib/action_controller/session/cookie_store.rb
index a2543c1..eed437a 100644
--- a/actionpack/lib/action_controller/session/cookie_store.rb
+++ b/actionpack/lib/action_controller/session/cookie_store.rb
@@ -97,21 +97,24 @@ module ActionController
 
         if !session_data.is_a?(AbstractStore::SessionHash) || session_data.send(:loaded?) || options[:expire_after]
           session_data.send(:load!) if session_data.is_a?(AbstractStore::SessionHash) && !session_data.send(:loaded?)
-          session_data = marshal(session_data.to_hash)
 
-          raise CookieOverflow if session_data.size > MAX
+          unless session_data.keys.reject {|k| k == :session_id }.empty?
+            marshaled_session_data = marshal(session_data.to_hash)
 
-          cookie = Hash.new
-          cookie[:value] = session_data
-          unless options[:expire_after].nil?
-            cookie[:expires] = Time.now + options[:expire_after]
-          end
+            raise CookieOverflow if marshaled_session_data.size > MAX
 
-          cookie = build_cookie(@key, cookie.merge(options))
-          unless headers[HTTP_SET_COOKIE].blank?
-            headers[HTTP_SET_COOKIE] << "\n#{cookie}"
-          else
-            headers[HTTP_SET_COOKIE] = cookie
+            cookie = Hash.new
+            cookie[:value] = marshaled_session_data
+            unless options[:expire_after].nil?
+              cookie[:expires] = Time.now + options[:expire_after]
+            end
+
+            cookie = build_cookie(@key, cookie.merge(options))
+            unless headers[HTTP_SET_COOKIE].blank?
+              headers[HTTP_SET_COOKIE] << "\n#{cookie}"
+            else
+              headers[HTTP_SET_COOKIE] = cookie
+            end
           end
         end
 
diff --git a/actionpack/test/controller/session/cookie_store_test.rb b/actionpack/test/controller/session/cookie_store_test.rb
index 5ef8eec..ff96b90 100644
--- a/actionpack/test/controller/session/cookie_store_test.rb
+++ b/actionpack/test/controller/session/cookie_store_test.rb
@@ -17,6 +17,11 @@ class CookieStoreTest < ActionController::IntegrationTest
       head :ok
     end
 
+    def session_access_buy_empty
+      session[:value]
+      render :text => ''
+    end
+    
     def persistent_session_id
       render :text => session[:session_id]
     end
@@ -110,6 +115,14 @@ class CookieStoreTest < ActionController::IntegrationTest
    end
   end
 
+  def test_empty_session_shouldnt_generate_cookie
+    with_test_route_set do
+      get '/session_access_buy_empty'
+      assert_response :success
+      assert_nil headers['Set-Cookie']
+    end
+  end
+  
   def test_getting_session_id
     with_test_route_set do
       cookies[SessionKey] = SignedBar