diff --git a/setup.rb b/setup.rb
index 16ffa7215..49f6bfca5 100644
--- a/setup.rb
+++ b/setup.rb
@@ -31,6 +31,12 @@ require 'rubygems/exceptions'
 
 Gem::CommandManager.instance.register_command :setup
 
+require 'rubygems/commands/setup_command'
+
+class Gem::Commands::SetupCommand
+  def install_default_bundler_gem(bin_dir); end
+end
+
 args = ARGV.clone
 if ENV["GEM_PREV_VER"]
   args = [ '--previous-version', ENV["GEM_PREV_VER"] ] + args