diff --git a/lib/sass/engine.rb b/lib/sass/engine.rb
index 2b2417a4..1f5a4cbd 100644
--- a/lib/sass/engine.rb
+++ b/lib/sass/engine.rb
@@ -408,7 +408,7 @@ END
         raise SyntaxError.new("Invalid variable \"#{arg}\".", @line) unless arg =~ Script::VALIDATE
         raise SyntaxError.new("Required arguments must not follow optional arguments \"#{arg}\".", @line) if default_arg_found && !default
         default = parse_script(default, :offset => line.offset + line.text.index(default)) if default
-        { :name => arg[1..-1], :default_value => default }
+        [arg[1..-1], default]
       end
       Tree::MixinDefNode.new(name, args, @options)
     end
diff --git a/lib/sass/tree/mixin_node.rb b/lib/sass/tree/mixin_node.rb
index 921183fa..fe6c3f68 100644
--- a/lib/sass/tree/mixin_node.rb
+++ b/lib/sass/tree/mixin_node.rb
@@ -18,14 +18,15 @@ Mixin #{@name} takes #{mixin.args.size} argument#{'s' if mixin.args.size != 1}
  but #{@args.size} #{@args.size == 1 ? 'was' : 'were'} passed.
 END
 
-      environment = mixin.args.zip(@args).inject(Sass::Environment.new(mixin.environment)) do |env, (arg, value)|
-        env.set_local_var(arg[:name],
+      environment = mixin.args.zip(@args).
+        inject(Sass::Environment.new(mixin.environment)) do |env, ((name, default), value)|
+        env.set_local_var(name,
           if value
             value.perform(environment)
-          elsif arg[:default_value]
-            arg[:default_value].perform(env)
+          elsif default
+            default.perform(env)
           end)
-        raise Sass::SyntaxError.new("Mixin #{@name} is missing parameter !#{arg[:name]}.") unless env.var(arg[:name])
+        raise Sass::SyntaxError.new("Mixin #{@name} is missing parameter !#{name}.") unless env.var(name)
         env
       end
       mixin.tree.map {|c| c.perform(environment)}.flatten