diff --git a/gems/lib/rake/extensiontask.rb b/gems/lib/rake/extensiontask.rb
index fdbe8d8874..0ab0cb7b50 100644
--- a/gems/lib/rake/extensiontask.rb
+++ b/gems/lib/rake/extensiontask.rb
@@ -8,5 +8,7 @@ module Rake
         puts "#{args.name} => #{args.prereqs.join(' ')}"
       end
     end
+
+    def lib_dir; end
   end
 end