diff --git a/.github/workflows/example.yml b/.github/workflows/example.yml
index 5a67e56..175d6b7 100644
--- a/.github/workflows/example.yml
+++ b/.github/workflows/example.yml
@@ -12,16 +12,20 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-18.04, ubuntu-20.04]
+        os:
+        - ubuntu-18.04
+        - ubuntu-20.04
+        - macos-10.15
     
     steps:
       - uses: actions/checkout@v1.0.0
 
-      - name: "Set up Spack"
+      - name: Set up Spack
         uses: ./
         with:
           os: ${{ matrix.os }}
+          ref: develop
       - run: spack --version
       - run: spack config blame config
       - run: spack install zlib
-      - run: which patchelf
\ No newline at end of file
+      - run: which patchelf
diff --git a/action.yml b/action.yml
index 790dea0..6e92b3d 100644
--- a/action.yml
+++ b/action.yml
@@ -1,21 +1,28 @@
-name: 'Setup Spack'
-description: 'Setup Spack and its dependencies'
+name: "Setup Spack"
+description: "Setup Spack and its dependencies"
 inputs:
   os:
-    description: 'Runner operating system (ubuntu-18.04, ubuntu20.04)'
+    description: "Operating system (ubuntu-18.04, ubuntu-20.04, macos-10.15)"
     required: true
+  ref:
+    description: "Version of Spack (develop, v0.16.2)"
+    required: false
+    default: develop
 runs:
   using: "composite"
   steps:
     - name: Install Spack's dependencies
       run: |
         curl -LfSs -o spack.tar.zstd https://github.com/haampie-spack/setup-spack/releases/download/develop/${{ inputs.os }}.tar.zst
-        tar --use-compress-program="zstd" -xf spack.tar.zstd -C ~/
+        TAR=tar
+        if [ "$RUNNER_OS" == macOS ]; then TAR=gtar; fi
+        $TAR --use-compress-program=zstd -xf spack.tar.zstd -C ~/
         echo "$HOME/.setup-spack/view/bin" >> $GITHUB_PATH
       shell: bash
     - name: Install Spack itself
       run: |
-        git clone --depth 5 https://github.com/spack/spack.git
+        git clone https://github.com/spack/spack.git
+        (cd spack && git checkout "${{ inputs.ref }}")
         echo "$PWD/spack/bin" >> $GITHUB_PATH
         mkdir ~/.spack
         echo "config:"                > ~/.spack/config.yaml
diff --git a/readme.md b/readme.md
index 0d2220d..185c004 100644
--- a/readme.md
+++ b/readme.md
@@ -15,13 +15,31 @@ jobs:
         os:
         - ubuntu-18.04
         - ubuntu-20.04
+        - macos-10.15
 
     steps:
       - uses: actions/checkout@v1.0.0
-      - name: "Set up Spack"
+      - name: Set up Spack
         uses: haampie-spack/setup-spack@v1
         with:
           os: ${{ matrix.os }}
-      - run: spack --version
-      - run: spack install zlib
-```
\ No newline at end of file
+          ref: develop
+      - run: |
+        spack --version
+        spack install zlib
+```
+
+
+
+## How is Spack bootstrapped?
+
+This environment is built
+
+https://github.com/haampie-spack/setup-spack/blob/rebuild-spack/spack.yaml
+
+and the binaries are uploaded as release assets to
+
+https://github.com/haampie-spack/setup-spack/releases/tag/develop
+
+Todo:
+- [ ] Add checksum verification
\ No newline at end of file