diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 2300f53..c0a8474 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -44,7 +44,7 @@ jobs:
         # does not claim; keep the two in lockstep.
         python-version: ["3.11", "3.12"]
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262  # v4
 
       - uses: actions/setup-python@v5
         with:
@@ -100,7 +100,7 @@ jobs:
       run:
         working-directory: impl/go
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262  # v4
 
       - uses: actions/setup-go@v5
         with:
@@ -119,7 +119,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 15
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262  # v4
 
       - uses: dtolnay/rust-toolchain@stable
 
@@ -162,7 +162,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 10
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262  # v4
 
       - uses: actions/setup-python@v5
         with:
@@ -230,7 +230,7 @@ jobs:
     runs-on: ubuntu-latest
     timeout-minutes: 20
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@11d5960a326750d5838078e36cf38b85af677262  # v4
 
       - uses: actions/setup-python@v5
         with: