diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 655953377..05d4af6a0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -16,7 +16,7 @@ jobs:
       matrix:
         compiler: [clang++-6.0, g++-10]
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
     - name: Install Dependencies
       # Boost must be installed only because the CMake version (3.12) can't
       # detect the installed Boost version (1.69)
@@ -37,7 +37,7 @@ jobs:
       matrix:
         compiler: [clang++, g++]
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
     - name: Install Dependencies
       # Boost must be installed only because the CMake version (3.12) can't
       # detect the installed Boost version (1.69)
@@ -64,7 +64,7 @@ jobs:
     needs: [linux-min]
     runs-on: windows-2022
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
     - name: Run Tests
       shell: powershell
       # Delete the exercises that require Boost to avoid issues with Windows setup.
@@ -80,7 +80,7 @@ jobs:
     needs: [linux-min]
     runs-on: macOS-latest
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
     - name: Install Boost
       run: brew install boost
     - name: Run Tests
diff --git a/.github/workflows/hello-world.yml b/.github/workflows/hello-world.yml
index 6787a9360..df37f33d7 100644
--- a/.github/workflows/hello-world.yml
+++ b/.github/workflows/hello-world.yml
@@ -21,7 +21,7 @@ jobs:
     name: Hello World Fails
     runs-on: ubuntu-22.04
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
     - name: Check Hello World Fails
       run: bin/check-hello-world.sh
       env:
diff --git a/.github/workflows/verify-code-formatting.yml b/.github/workflows/verify-code-formatting.yml
index 2f92d967b..82a99dd89 100644
--- a/.github/workflows/verify-code-formatting.yml
+++ b/.github/workflows/verify-code-formatting.yml
@@ -21,7 +21,7 @@ jobs:
     runs-on: [ubuntu-22.04]
     steps:
       - name: "Checkout code"
-        uses: actions/checkout@v4
+        uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
 
       - name: "Verify formatting of all files"
         if: github.ref == 'refs/heads/master'