diff --git a/.gitea/workflows/masterplan-lock.yml b/.gitea/workflows/masterplan-lock.yml
index e3193216..d203020f 100644
--- a/.gitea/workflows/masterplan-lock.yml
+++ b/.gitea/workflows/masterplan-lock.yml
@@ -16,6 +16,6 @@ jobs:
   check:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: https://git.siax.io/actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # mirrored, immutable
       - name: Masterplan lock check
         run: sh scripts/check-masterplan-lock.sh