diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e223b0f..23714b0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -8,10 +8,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout main
-        uses: actions/checkout@v2
-        
+        uses: actions/checkout@ee0669bd1cc54295c223e0bb666b733df41de1c5 # v2
+
       - name: Install Python 3
-        uses: actions/setup-python@v2
+        uses: actions/setup-python@e9aba2c848f5ebd159c070c61ea2c4e2b122355e # v2
         with:
           python-version: 3.8
           
@@ -25,7 +25,7 @@ jobs:
         run: echo "::set-output name=dir::$(pip cache dir)"
 
       - name: Cache dependencies
-        uses: actions/cache@v2
+        uses: actions/cache@8492260343ad570701412c2f464a5877dc76bace # v2
         with:
           path: ${{ steps.pip-cache.outputs.dir }}
           key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt', '**/requirements-sphinx.txt') }}
@@ -58,7 +58,7 @@ jobs:
 
       - name: Deploy site
         if: github.ref == 'refs/heads/main'
-        uses: peaceiris/actions-gh-pages@v3
+        uses: peaceiris/actions-gh-pages@373f7f263a76c20808c831209c920827a82a2847 # v3
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: root