--- ./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'
@@ -79,5 +79,5 @@
   # Turn on `enable_debug` for better debugging
   # conf.enable_debug
-  conf.enable_bintest
-  conf.enable_test
+  # conf.enable_bintest
+  # conf.enable_test
 end