diff --git a/.github/workflows/doc.yml b/.github/workflows/doc.yml
index b7737ea7..18e518a2 100644
--- a/.github/workflows/doc.yml
+++ b/.github/workflows/doc.yml
@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-20.04
 
     steps:
-    - uses: actions/checkout@v3
+    - uses: actions/checkout@8e5e7e5ab8b370d6c329ec480221332ada57f0ab # v3.5.2
 
     - name: Add ubuntu mirrors
       run: |