--- ./mruby/build_config/default.rb
+++ ./mruby/build_config/default.rb
@@ -1,6 +1,18 @@
 MRuby::Build.new do |conf|
   # load specific toolchain settings
-  conf.toolchain
+  conf.toolchain :gcc
+
+  conf.cc do |cc|
+    cc.command = ENV['CC']
+  end
+
+  conf.cxx do |cxx|
+    cxx.command = ENV['CXX']
+  end
+
+  conf.linker do |linker|
+    linker.command = ENV['CXX']
+  end
 
   # Use mrbgems
   # conf.gem 'examples/mrbgems/ruby_extension_example'
@@ -16,6 +28,10 @@
   # include the GEM box
   conf.gembox 'default'
 
+  conf.gem '../mgems/mruby-env'
+  conf.gem '../mgems/mruby-process'
+  conf.gem '../mgems/mruby-marshal-c'
+
   # C compiler settings
   # conf.cc do |cc|
   #   cc.command = ENV['CC'] || 'gcc'