diff --git a/.github/workflows/ci-cogent3-dev.yml b/.github/workflows/ci-cogent3-dev.yml
index a6a4ab8..ecd72a7 100644
--- a/.github/workflows/ci-cogent3-dev.yml
+++ b/.github/workflows/ci-cogent3-dev.yml
@@ -12,7 +12,7 @@ jobs:
     if: github.repository == 'HuttleyLab/MutationMotif'
 
     steps:
-      - uses: "actions/checkout@v6"
+      - uses: "actions/checkout@v6.0.3"
         with:
           fetch-depth: 0
 
diff --git a/.github/workflows/linters.yml b/.github/workflows/linters.yml
index 9ac1d1e..859e8e4 100644
--- a/.github/workflows/linters.yml
+++ b/.github/workflows/linters.yml
@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     if: github.repository == 'HuttleyLab/MutationMotif'
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v6.0.3
 
       - name: Install uv
         uses: astral-sh/setup-uv@v7
diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index ea32cd7..e15604d 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -10,7 +10,7 @@ jobs:
       matrix:
         python-version: ["3.11", "3.12", "3.13", "3.14"]
     steps:
-      - uses: "actions/checkout@v6"
+      - uses: "actions/checkout@v6.0.3"
         with:
           fetch-depth: 0
 
@@ -30,7 +30,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v6
+      - uses: actions/checkout@v6.0.3
         with:
           fetch-depth: 0
 
diff --git a/.github/workflows/testing_develop.yml b/.github/workflows/testing_develop.yml
index e3644c8..153219c 100644
--- a/.github/workflows/testing_develop.yml
+++ b/.github/workflows/testing_develop.yml
@@ -19,7 +19,7 @@ jobs:
         python-version: ["3.11", "3.14"]
 
     steps:
-      - uses: "actions/checkout@v6"
+      - uses: "actions/checkout@v6.0.3"
         with:
           fetch-depth: 0