diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7be5de0e4..1c996dcc4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,7 @@
 ## 0.6.4 (unreleased)
 
+  - Top config class is now available in all `Vagrant::Config::Base`
+    subclasses, which is useful for config validation.
   - Subcommand help shows proper full command in task listing. [GH-168]
   - SSH gives error message if `ssh` binary is not found. [GH-161]
   - SSH gives proper error message if VM is not running. [GH-167]
diff --git a/lib/vagrant/config.rb b/lib/vagrant/config.rb
index 2acf68c9b..b9748748d 100644
--- a/lib/vagrant/config.rb
+++ b/lib/vagrant/config.rb
@@ -137,6 +137,7 @@ module Vagrant
         self.class.configures_list.each do |key, klass|
           config = klass.new
           config.env = env
+          config.top = self
           instance_variable_set("@#{key}".to_sym, config)
         end
 
diff --git a/lib/vagrant/config/base.rb b/lib/vagrant/config/base.rb
index 57e10f796..2f90ffff6 100644
--- a/lib/vagrant/config/base.rb
+++ b/lib/vagrant/config/base.rb
@@ -4,8 +4,12 @@ module Vagrant
     # basic things such as the environment instance variable which all
     # config classes need as well as a basic `to_json` implementation.
     class Base
+      # {Environment} that this config belongs to
       attr_accessor :env
 
+      # {Top} of this configuration stack
+      attr_accessor :top
+
       # Registers a subclass with the Vagrant configuration system so
       # that it can then be used in Vagrantfiles.
       #
@@ -58,7 +62,7 @@ module Vagrant
       # Returns the instance variables as a hash of key-value pairs.
       def instance_variables_hash
         instance_variables.inject({}) do |acc, iv|
-          acc[iv.to_s[1..-1]] = instance_variable_get(iv) unless iv.to_sym == :@env
+          acc[iv.to_s[1..-1]] = instance_variable_get(iv) unless [:@env, :@top].include?(iv.to_sym)
           acc
         end
       end
diff --git a/test/vagrant/config/base_test.rb b/test/vagrant/config/base_test.rb
index 858238c17..ee184a030 100644
--- a/test/vagrant/config/base_test.rb
+++ b/test/vagrant/config/base_test.rb
@@ -47,6 +47,12 @@ class ConfigBaseTest < Test::Unit::TestCase
         hash = @base.instance_variables_hash
         assert !hash.has_key?(:env)
       end
+
+      should "not include top in the JSON hash" do
+        @base.top = "FOO"
+        hash = @base.instance_variables_hash
+        assert !hash.has_key?(:top)
+      end
     end
   end
 end
diff --git a/test/vagrant/config_test.rb b/test/vagrant/config_test.rb
index 37dd3f628..c57466fd8 100644
--- a/test/vagrant/config_test.rb
+++ b/test/vagrant/config_test.rb
@@ -167,6 +167,10 @@ class ConfigTest < Test::Unit::TestCase
           klass = mock("klass#{i}")
           instance = mock("instance#{i}")
           instance.expects(:env=).with(env)
+          instance.expects(:top=).with() do |top|
+            assert top.is_a?(@klass::Top)
+            true
+          end
           klass.expects(:new).returns(instance)
           @configures_list[key] = klass
         end
@@ -179,6 +183,7 @@ class ConfigTest < Test::Unit::TestCase
         klass = mock("klass")
         instance = mock("instance")
         instance.stubs(:env=)
+        instance.stubs(:top=)
         klass.expects(:new).returns(instance)
         @klass::Top.configures(key, klass)