diff --git a/.github/actions/install-homebrew-valgrind/action.yml b/.github/actions/install-homebrew-valgrind/action.yml
new file mode 100644
index 0000000000..094ff891f7
--- /dev/null
+++ b/.github/actions/install-homebrew-valgrind/action.yml
@@ -0,0 +1,33 @@
+name: "Install Valgrind"
+description: "Install Homebrew's Valgrind package and cache it."
+runs:
+  using: "composite"
+  steps:
+    - run: |
+        brew tap LouisBrunner/valgrind
+        brew fetch --HEAD LouisBrunner/valgrind/valgrind
+        echo "CI_HOMEBREW_CELLAR_VALGRIND=$(brew --cellar valgrind)" >> "$GITHUB_ENV"
+      shell: bash
+
+    - run: |
+        sw_vers > valgrind_fingerprint
+        brew --version >> valgrind_fingerprint
+        git -C "$(brew --cache)/valgrind--git" rev-parse HEAD >> valgrind_fingerprint
+        cat valgrind_fingerprint
+      shell: bash
+
+    - uses: actions/cache@v3
+      id: cache
+      with:
+        path: ${{ env.CI_HOMEBREW_CELLAR_VALGRIND }}
+        key: ${{ github.job }}-valgrind-${{ hashFiles('valgrind_fingerprint') }}
+
+    - if: steps.cache.outputs.cache-hit != 'true'
+      run: |
+        brew install --HEAD LouisBrunner/valgrind/valgrind
+      shell: bash
+
+    - if: steps.cache.outputs.cache-hit == 'true'
+      run: |
+        brew link valgrind
+      shell: bash
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 441cf41ee9..d242061179 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -574,7 +574,7 @@ jobs:
         run: env
         if: ${{ always() }}
 
-  macos-native:
+  macos-ventura:
     name: "x86_64: macOS Ventura"
     # See: https://github.com/actions/runner-images#available-images.
     runs-on: macos-13 # Use M1 once available https://github.com/github/roadmap/issues/528
@@ -632,6 +632,61 @@ jobs:
         run: env
         if: ${{ always() }}
 
+  macos-monterey:
+    name: "x86_64: macOS Monterey, ctime_tests"
+    # See: https://github.com/actions/runner-images#available-images.
+    runs-on: macos-12
+
+    env:
+      CC: 'clang'
+      HOMEBREW_NO_AUTO_UPDATE: 1
+      HOMEBREW_NO_INSTALL_CLEANUP: 1
+
+    strategy:
+      fail-fast: false
+      matrix:
+        env_vars:
+          - { WIDEMUL: 'int64',  RECOVERY: 'yes', ECDH: 'yes', SCHNORRSIG: 'yes', ELLSWIFT: 'yes' }
+          - { WIDEMUL: 'int64',  RECOVERY: 'yes', ECDH: 'yes', SCHNORRSIG: 'yes', ELLSWIFT: 'yes', CC: 'gcc' }
+          - { WIDEMUL: 'int128_struct', ECMULTGENPRECISION: 2, ECMULTWINDOW: 4 }
+          - { WIDEMUL: 'int128',                  ECDH: 'yes', SCHNORRSIG: 'yes', ELLSWIFT: 'yes' }
+          - { WIDEMUL: 'int128', RECOVERY: 'yes',              SCHNORRSIG: 'yes' }
+          - { WIDEMUL: 'int128', RECOVERY: 'yes', ECDH: 'yes', SCHNORRSIG: 'yes', ELLSWIFT: 'yes', CC: 'gcc' }
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Install Homebrew packages
+        run: |
+          brew install automake libtool gcc
+          ln -s $(brew --prefix gcc)/bin/gcc-?? /usr/local/bin/gcc
+
+      - name: Install and cache Valgrind
+        uses: ./.github/actions/install-homebrew-valgrind
+
+      - name: CI script
+        env: ${{ matrix.env_vars }}
+        run: ./ci/ci.sh
+
+      - run: cat tests.log || true
+        if: ${{ always() }}
+      - run: cat noverify_tests.log || true
+        if: ${{ always() }}
+      - run: cat exhaustive_tests.log || true
+        if: ${{ always() }}
+      - run: cat ctime_tests.log || true
+        if: ${{ always() }}
+      - run: cat bench.log || true
+        if: ${{ always() }}
+      - run: cat config.log || true
+        if: ${{ always() }}
+      - run: cat test_env.log || true
+        if: ${{ always() }}
+      - name: CI env
+        run: env
+        if: ${{ always() }}
+
   win64-native:
     name: ${{ matrix.configuration.job_name }}
     # See: https://github.com/actions/runner-images#available-images.