diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 470ab168..92dd0b45 100755
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -13,10 +13,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os:
-          #- ubuntu-latest
-          - macos-latest
-          #- windows-latest
+        os: [ubuntu-latest, macos-latest, windows-latest]
         resolver:
         # Missing some packages now
         #- "--resolver nightly"
@@ -34,6 +31,12 @@ jobs:
     steps:
       - name: Clone project
         uses: actions/checkout@v2
+      - name: Install LLVM 12
+        run: |
+          brew install llvm@12
+          echo "$(brew --prefix)/opt/llvm/bin"                >> "${GITHUB_PATH}"
+          echo LDFLAGS="-L$(brew --prefix)/opt/llvm/lib"      >> "${GITHUB_ENV}"
+          echo CPPFLAGS="-I$(brew --prefix)/opt/llvm/include" >> "${GITHUB_ENV}"
       - name: Setup Haskell
         uses: haskell-actions/setup@v2.7.5
         with: