diff --git a/.github/workflows/env-checks.yml b/.github/workflows/env-checks.yml
index f43ea60..d0a5f4b 100644
--- a/.github/workflows/env-checks.yml
+++ b/.github/workflows/env-checks.yml
@@ -47,7 +47,7 @@ jobs:
     # Steps represent a sequence of tasks that will be executed as part of the job
     steps:
       # checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683  # v4.2.2
 
       # remove the Python version from the file for testing
       - name: strip hardcoded Python version from environment for testing
diff --git a/.github/workflows/publish-slides.yml b/.github/workflows/publish-slides.yml
index f26f986..1a3af36 100644
--- a/.github/workflows/publish-slides.yml
+++ b/.github/workflows/publish-slides.yml
@@ -29,17 +29,17 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683  # v4.2.2
       - name: Setup Pages
-        uses: actions/configure-pages@v5
+        uses: actions/configure-pages@983d7736d9b0ae728b81ab479565c72886d7745b  # v5.0.0
       - name: Package files
         run: |
           mkdir public && \
             cp slides/html/workshop.slides.html public/index.html;
       - name: Upload artifact
-        uses: actions/upload-pages-artifact@v3
+        uses: actions/upload-pages-artifact@56afc609e74202658d3ffba0e8f6dda462b719fa  # v3.0.1
         with:
           path: public
       - name: Deploy to GitHub Pages
         id: deployment
-        uses: actions/deploy-pages@v4
+        uses: actions/deploy-pages@d6db90164ac5ed86f2b6aed7e0febac5b3c0c03e  # v4.0.5