diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index b07989ee..8cbdf013 100755
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -10,12 +10,22 @@ jobs:
   macos-latest:
     name: macos-latest
     runs-on: macos-latest
+    strategy:
+      matrix:
+        os:
+          - macos-latest
+        resolver:
+          20.26
+          19.33
+          18.28
     steps:
       - name: Install LLVM 12
-        run: brew install llvm@12
-          #echo "/opt/homebrew/opt/llvm@12/bin" >> "${GITHUB_PATH}"
-          #echo LDFLAGS="-L/opt/homebrew/opt/llvm@12/lib" >> "${GITHUB_ENV}"
-          #echo CPPFLAGS="-I/opt/homebrew/opt/llvm@12/include" >> "${GITHUB_ENV}"
+        if: ${{ matrix.os == macos-latest && matrix.resolver < 20 }}
+        run: |
+          brew install llvm@12
+          echo "/opt/homebrew/opt/llvm@12/bin" >> "${GITHUB_PATH}"
+          echo LDFLAGS="-L/opt/homebrew/opt/llvm@12/lib" >> "${GITHUB_ENV}"
+          echo CPPFLAGS="-I/opt/homebrew/opt/llvm@12/include" >> "${GITHUB_ENV}"
       - name: Setup Haskell
         uses: haskell-actions/setup@v2.7
         with:
@@ -30,9 +40,7 @@ jobs:
         run: |
             set -ex
             stack --version
-            for resolver in 18.28 19.33
-            do stack test --fast --no-terminal --resolver=lts-$resolver
-            done
+            stack test --fast --no-terminal --resolver=${{ matrix.resolver }}
 
 #  macos-13:
 #    name: macos-13