diff --git a/lib/mongoid/extensions.rb b/lib/mongoid/extensions.rb
index <HASH>..<HASH> 100644
--- a/lib/mongoid/extensions.rb
+++ b/lib/mongoid/extensions.rb
@@ -20,7 +20,9 @@ class Array #:nodoc
 end
 
 class Binary; end #:nodoc:
-class Boolean; end #:nodoc:
+unless defined?(Boolean)
+  class Boolean; end
+end
 
 class FalseClass #:nodoc
   include Mongoid::Extensions::FalseClass::Equality
Don't try to declare the Boolean class if it already exists: just make it include the Boolean extension. This prevents conflict with the Ripple gem. All specs pass.