diff --git a/tool/sync_default_gems.rb b/tool/sync_default_gems.rb
index 8f8e93815c..04b9fe7877 100644
--- a/tool/sync_default_gems.rb
+++ b/tool/sync_default_gems.rb
@@ -118,6 +118,7 @@ def sync_default_gems(gem)
       'lib/rdoc/rd/inline_parser.ry' => 'lib/rdoc/rd/inline_parser.rb'
     }
     Dir.chdir(upstream) do
+      `bundle install`
       parser_files.each_value do |dst|
         `bundle exec rake #{dst}`
       end