diff --git a/spec/instructions/prefix_spec.rb b/spec/instructions/prefix_spec.rb
index e3df4ac..2ef7934 100644
--- a/spec/instructions/prefix_spec.rb
+++ b/spec/instructions/prefix_spec.rb
@@ -1,10 +1,6 @@
 require 'spec_helper'
 
 describe Waterfoul::CPU do
-  before do
-    $mmu = double :mmu
-  end
-
   subject { Waterfoul::CPU.new }
 
   # SWAP n