diff --git a/build_config/host-cxx.rb b/build_config/host-cxx.rb
index 15cb0c347..5dc37edd0 100644
--- a/build_config/host-cxx.rb
+++ b/build_config/host-cxx.rb
@@ -1,4 +1,4 @@
-MRuby::Build.new do |conf|
+MRuby::Build.new('host-cxx') do |conf|
   conf.toolchain
 
   # include the default GEMs