diff --git a/.github/workflows/ci-linux.yml b/.github/workflows/ci-linux.yml
index f6c269978..56093a067 100644
--- a/.github/workflows/ci-linux.yml
+++ b/.github/workflows/ci-linux.yml
@@ -35,7 +35,8 @@ jobs:
       fail-fast: true
     env:
       CACHE_DIR: ${{ github.workspace }}/.container-cache
-      CACHE_KEY: linux-build-test-cpp-asserts-manylinux-v2-${{ github.event.number || github.ref_name }}
+      # either the PR number or `branch-N` where N always increments
+      CACHE_KEY: linux-build-test-cpp-asserts-manylinux-v2-${{ github.event.number || format('{0}-{1}', github.ref_name, github.run_number) }}
     steps:
       - name: Set unified TZ
         uses: szenius/set-timezone@v2.0
diff --git a/.github/workflows/ci-macos.yml b/.github/workflows/ci-macos.yml
index a94d84b69..a86d11c56 100644
--- a/.github/workflows/ci-macos.yml
+++ b/.github/workflows/ci-macos.yml
@@ -30,7 +30,7 @@ jobs:
         runs-on: [macos-12, macos-14]
     env:
       CACHE_DIR: ${{ github.workspace }}/.container-cache
-      CACHE_KEY: ${{ matrix.runs-on }}-build-test-cpp-asserts-v1-${{ github.event.number || github.ref_name }}
+      CACHE_KEY: ${{ matrix.runs-on }}-build-test-cpp-asserts-v1-${{ github.event.number || format('{0}-{1}', github.ref_name, github.run_number) }}
     steps:
       - name: Set unified TZ
         uses: szenius/set-timezone@v2.0
diff --git a/.github/workflows/ci-windows.yml b/.github/workflows/ci-windows.yml
index 07e5e3248..d4e3c3899 100644
--- a/.github/workflows/ci-windows.yml
+++ b/.github/workflows/ci-windows.yml
@@ -33,7 +33,7 @@ jobs:
       fail-fast: true
     env:
       CACHE_DIR: ${{ github.workspace }}/.container-cache
-      CACHE_KEY: windows-build-test-cpp-asserts-v1-${{ github.event.number || github.ref_name }}
+      CACHE_KEY: windows-build-test-cpp-asserts-v1-${{ github.event.number || format('{0}-{1}', github.ref_name, github.run_number) }}
     steps:
       - name: Set unified TZ
         uses: szenius/set-timezone@v2.0