diff --git a/lib/vagrant/config/base.rb b/lib/vagrant/config/base.rb
index 2cc31d82b..dda537983 100644
--- a/lib/vagrant/config/base.rb
+++ b/lib/vagrant/config/base.rb
@@ -25,6 +25,20 @@ module Vagrant
         end
       end
 
+      # Merge another configuration object into this one.
+      #
+      # @param [Object] other The other configuration object to merge from,
+      #   this must be the same type of object as this one.
+      # @return [Object] The merged object.
+      def merge(other)
+        result = self.class.new
+        instance_variables_hash.merge(other.instance_variables_hash).each do |key, value|
+          result.instance_variable_set("@#{key}".to_sym, value)
+        end
+
+        result
+      end
+
       # Called by {Top} after the configuration is loaded to validate
       # the configuaration objects. Subclasses should implement this
       # method and add any errors to the `errors` object given.
@@ -54,7 +68,7 @@ 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 == :@top
+          acc[iv.to_s[1..-1]] = instance_variable_get(iv)
           acc
         end
       end
diff --git a/lib/vagrant/config/loader.rb b/lib/vagrant/config/loader.rb
index fe92dc61b..fc588df1e 100644
--- a/lib/vagrant/config/loader.rb
+++ b/lib/vagrant/config/loader.rb
@@ -20,6 +20,7 @@ module Vagrant
         @logger  = Log4r::Logger.new("vagrant::config::loader")
         @sources = {}
         @proc_cache = {}
+        @config_cache = {}
       end
 
       # Set the configuration data for the given name.
@@ -70,21 +71,26 @@ module Vagrant
         end
 
         # Create the top-level configuration which will hold all the config.
-        top = Top.new
+        result = Top.new
 
         @load_order.each do |key|
           next if !@sources.has_key?(key)
 
           @sources[key].each do |proc|
-            @logger.debug("Loading from: #{key}")
+            if !@config_cache.has_key?(proc)
+              @logger.debug("Loading from: #{key} (evaluating)")
+              current = Top.new
+              proc.call(current)
+              @config_cache[proc] = current
+            end
 
-            # Call each proc with the top-level configuration.
-            proc.call(top)
+            # Merge in the results of this proc's configuration
+            result = result.merge(@config_cache[proc])
           end
         end
 
         @logger.debug("Configuration loaded successfully")
-        top
+        result
       end
 
       protected
diff --git a/test/unit/vagrant/config/loader_test.rb b/test/unit/vagrant/config/loader_test.rb
index 86ea2b5a1..4d5d2e20f 100644
--- a/test/unit/vagrant/config/loader_test.rb
+++ b/test/unit/vagrant/config/loader_test.rb
@@ -22,6 +22,27 @@ describe Vagrant::Config::Loader do
     config.vagrant.dotfile_name.should == "foo"
   end
 
+  it "should only run the same proc once" do
+    count = 0
+    proc = Proc.new do |config|
+      config.vagrant.dotfile_name = "foo"
+      count += 1
+    end
+
+    instance.load_order = [:proc]
+    instance.set(:proc, proc)
+
+    5.times do
+      result = instance.load
+
+      # Verify the config result
+      result.vagrant.dotfile_name.should == "foo"
+
+      # Verify the count is only one
+      count.should == 1
+    end
+  end
+
   it "should only load configuration files once" do
     $_config_data = 0
 
@@ -35,19 +56,6 @@ describe Vagrant::Config::Loader do
     $_config_data.should == 1
   end
 
-  it "should clear cache on setting to a new value" do
-    $_config_data = 0
-
-    instance.load_order = [:proc]
-    instance.set(:proc, temporary_file("$_config_data += 1"))
-    5.times { instance.load }
-
-    instance.set(:proc, temporary_file("$_config_data += 1"))
-    5.times { instance.load }
-
-    $_config_data.should == 2
-  end
-
   it "should not clear the cache if setting to the same value multiple times" do
     $_config_data = 0