diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 05ac469..3301ca1 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -67,12 +67,9 @@ jobs:
         run: make
       - name: install
         run: sudo make install
-      - working-directory: vendor/mruby
-        name: build config
-        run: cp ../../pkgs/mruby/build_config.rb build_config/default.rb
       - working-directory: vendor/mruby
         name: test
-        run: rake test
+        run: MRUBY_CONFIG=../../pkgs/mruby/build_config.rb rake test
       - working-directory: pkgs/mruby
         name: cppcheck
         run: cppcheck --quiet --error-exitcode=1 --std=c99 --enable=warning,style,performance,portability .
diff --git a/pkgs/mruby/.gitignore b/pkgs/mruby/.gitignore
new file mode 100644
index 0000000..cffc8cc
--- /dev/null
+++ b/pkgs/mruby/.gitignore
@@ -0,0 +1 @@
+/build_config.rb.lock
diff --git a/pkgs/mruby/build_config.rb b/pkgs/mruby/build_config.rb
index a386dc9..a2ae5ef 100644
--- a/pkgs/mruby/build_config.rb
+++ b/pkgs/mruby/build_config.rb
@@ -1,5 +1,5 @@
 MRuby::Build.new do |conf|
   conf.toolchain
   conf.enable_test
-  conf.gem '../../pkgs/mruby'
+  conf.gem '.'
 end