diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index b3290657..53f6b392 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -28,7 +28,7 @@ jobs:
       uses: fabiocaccamo/create-matrix-action@v4
       with:
         matrix: |
-          os {linux},   cpu {amd64}, builder {ubuntu-latest},  tests {all},         nim_version {${{ env.nim_version }}}, shell {bash --noprofile --norc -e -o pipefail}
+          os {linux},   cpu {amd64}, builder {ubuntu-20.04},   tests {all},         nim_version {${{ env.nim_version }}}, shell {bash --noprofile --norc -e -o pipefail}
           os {macos},   cpu {amd64}, builder {macos-13},       tests {all},         nim_version {${{ env.nim_version }}}, shell {bash --noprofile --norc -e -o pipefail}
           os {windows}, cpu {amd64}, builder {windows-latest}, tests {unittest},    nim_version {${{ env.nim_version }}}, shell {msys2}
           os {windows}, cpu {amd64}, builder {windows-latest}, tests {contract},    nim_version {${{ env.nim_version }}}, shell {msys2}
@@ -43,7 +43,7 @@ jobs:
       cache_nonce: ${{ needs.matrix.outputs.cache_nonce }}
 
   coverage:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     steps:
       - name: Checkout sources
         uses: actions/checkout@v4
diff --git a/.github/workflows/nim-matrix.yml b/.github/workflows/nim-matrix.yml
index 579ee6a5..2d822641 100644
--- a/.github/workflows/nim-matrix.yml
+++ b/.github/workflows/nim-matrix.yml
@@ -20,7 +20,7 @@ jobs:
       uses: fabiocaccamo/create-matrix-action@v4
       with:
         matrix: |
-          os {linux}, cpu {amd64}, builder {ubuntu-latest}, tests {all}, nim_version {${{ env.nim_version }}}, shell {bash --noprofile --norc -e -o pipefail}
+          os {linux}, cpu {amd64}, builder {ubuntu-20.04}, tests {all}, nim_version {${{ env.nim_version }}}, shell {bash --noprofile --norc -e -o pipefail}
 
   build:
     needs: matrix