diff --git a/.github/workflows/haskell.yml b/.github/workflows/haskell.yml
index b1c89d2..7a65c96 100644
--- a/.github/workflows/haskell.yml
+++ b/.github/workflows/haskell.yml
@@ -19,15 +19,15 @@ jobs:
     env:
       CONFIG: "--enable-tests"
     steps:
-      - uses: actions/checkout@v3
-      - uses: haskell-actions/setup@v2
+      - uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744 # v3.6.0
+      - uses: haskell-actions/setup@7909071ceec0344debcc968c6c7a96a52e8dd0d7 # v2.8.1
         id: setup-haskell-cabal
         with:
           ghc-version: ${{ matrix.ghc }}
           cabal-version: ${{ matrix.cabal }}
       - run: cabal v2-update
       - run: cabal v2-freeze $CONFIG
-      - uses: actions/cache@v3
+      - uses: actions/cache@2f8e54208210a422b2efd51efaa6bd6d7ca8920f # v3.4.3
         with:
           path: |
             ${{ steps.setup-haskell-cabal.outputs.cabal-store }}
diff --git a/.github/workflows/nix-checks.yaml b/.github/workflows/nix-checks.yaml
index 3970f49..9fe7b41 100644
--- a/.github/workflows/nix-checks.yaml
+++ b/.github/workflows/nix-checks.yaml
@@ -8,13 +8,13 @@ jobs:
   check_fourmolu:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
       - name: Install Nix
-        uses: cachix/install-nix-action@v27
+        uses: cachix/install-nix-action@ba0dd844c9180cbf77aa72a116d6fbc515d0e87b # V27
         with:
           extra_nix_config: |
             extra-experimental-features = nix-command flakes
-      - uses: cachix/cachix-action@v15
+      - uses: cachix/cachix-action@ad2ddac53f961de1989924296a1f236fcfbaa4fc # v15
         with:
           name: slack-web
           authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'