diff --git a/lib/middleman-syntax/haml_monkey_patch.rb b/lib/middleman-syntax/haml_monkey_patch.rb
index 91e9497..826d8b1 100644
--- a/lib/middleman-syntax/haml_monkey_patch.rb
+++ b/lib/middleman-syntax/haml_monkey_patch.rb
@@ -1,9 +1,7 @@
-# If Haml is around, define a :code filter that can be used to more conveniently output highlighted code.
-if defined? Haml
+if defined? Haml && Gem::Version.new(Haml::VERSION) >= Gem::Version.new("6.0.0.beta.1")
   module Haml
-    module Filters
-      module Code
-        include Base
+    class Filters
+      class Code < Base
 
         def render(code)
           code = code.rstrip