diff --git a/.github/workflows/ci-notify-slack.yml b/.github/workflows/ci-notify-slack.yml
index fd84dbe..d15a875 100644
--- a/.github/workflows/ci-notify-slack.yml
+++ b/.github/workflows/ci-notify-slack.yml
@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
 
       - name: Sanitize PR title
         id: sanitize
diff --git a/.github/workflows/pocket-ic-server-action-test.yml b/.github/workflows/pocket-ic-server-action-test.yml
index 76b39d6..a4ee436 100644
--- a/.github/workflows/pocket-ic-server-action-test.yml
+++ b/.github/workflows/pocket-ic-server-action-test.yml
@@ -38,7 +38,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4.3.1
       - name: Install latest PocketIC server and check its version
         if: "${{ matrix.version == '' }}"
         uses: ./