diff --git a/.github/workflows/ruby.yml b/.github/workflows/ruby.yml
index a873e75..3a7559d 100644
--- a/.github/workflows/ruby.yml
+++ b/.github/workflows/ruby.yml
@@ -11,10 +11,10 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-latest ]
+        os: [ ubuntu-latest, windows-latest, macos-latest ]
         ruby: [ jruby-9.4.12.0, jruby-head ]
 
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
 
     steps:
     - uses: actions/checkout@v2
diff --git a/Makefile b/Makefile
index 50cb8f8..6ef2844 100644
--- a/Makefile
+++ b/Makefile
@@ -100,7 +100,7 @@ include $(SUB_IMPLMK)
 # Pick conf based on OS. for mingw64, must manually override for now.
 ifeq ($(OS),Windows_NT)
 CC=gcc
-CONF=mingw
+CONF=mingw64
 else
 CONF=unix
 endif
diff --git a/spec/launcher_spec.rb b/spec/launcher_spec.rb
index 1478292..d97b0b6 100644
--- a/spec/launcher_spec.rb
+++ b/spec/launcher_spec.rb
@@ -1,8 +1,9 @@
 require 'tmpdir'
+require 'rbconfig'
 require File.expand_path('../spec_helper.rb', __FILE__)
 load File.expand_path('../../lib/jruby-launcher.rb', __FILE__)
 
-describe "JRuby native launcher", if: /Windows/.match?(ENV_JAVA['os.name']) do
+describe "JRuby native launcher", if: /mswin/.match?(RbConfig::CONFIG['host_os']) do
   it "should run org.jruby.Main" do
     jruby_launcher_args("").last.should == "org/jruby/Main"
   end