diff --git a/build_config.rb b/build_config.rb
index d379c7c..098ba1b 100644
--- a/build_config.rb
+++ b/build_config.rb
@@ -2,6 +2,7 @@ MRuby::CrossBuild.new ENV.fetch 'BUILD_NAME' do |conf|
   conf.toolchain :gcc
 
   conf.gem core: 'mruby-compiler'
+  conf.gembox 'stdlib'
 
   conf.cc.flags      <<
     '-Wall'          <<
diff --git a/rootfs/boot/hello.rb b/rootfs/boot/hello.rb
index e7a14ea..06ecfc5 100644
--- a/rootfs/boot/hello.rb
+++ b/rootfs/boot/hello.rb
@@ -1,4 +1,4 @@
-hello = 'Hello, World!'
-works = 'Ruby modules work!'
-s = [hello, works].join ' '
+hello = 'Hello, World'
+works = 'Ruby modules work'
+s = [hello, works].map { |s| "#{s}!" }.join ' '
 console_puts s