diff --git a/.circleci/config.yml b/.circleci/config.yml
index 5fc6d40897..93410a7c81 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -28,7 +28,19 @@ jobs:
             pixi run --as-is esmvaltool -- --help
             pixi run --as-is esmvaltool config list
             pixi run --as-is esmvaltool config show
+      - run:
+          name: Set the branch name for upload to Codecov
+          command: |
+            # Specify an "unprotected" branch name when the pull request comes
+            # from a fork: https://docs.codecov.com/docs/codecov-tokens#when-do-i-need-a-token
+            branch="$(git branch --show-current)"
+            prefix="${CIRCLE_PR_USERNAME}/${CIRCLE_PR_REPONAME}"
+            if [ -z "$CODECOV_TOKEN" ] && [ "${prefix}" != "${CIRCLE_PROJECT_USERNAME}/${CIRCLE_PROJECT_REPONAME}" ]; then
+              branch="${prefix}:${branch}"
+            fi
+            echo "export CODECOV_BRANCH=${branch}" >> $BASH_ENV
       - codecov/upload:
+          branch: "${CODECOV_BRANCH}"
           files: "test-reports/coverage.xml"
           disable_search: true
       - store_test_results:
diff --git a/.github/workflows/run-tests-fork.yml b/.github/workflows/run-tests-fork.yml
deleted file mode 100644
index 6d80e83e9f..0000000000
--- a/.github/workflows/run-tests-fork.yml
+++ /dev/null
@@ -1,37 +0,0 @@
----
-name: Test and Cov Fork PR
-
-permissions: {}
-
-# runs only on a forked PR targeting ESMValCore main
-on:
-  pull_request:
-    branches:
-      - main
-
-defaults:
-  run:
-    shell: pixi run bash -e {0}
-
-jobs:
-  test:
-    runs-on: ubuntu-latest
-    # run action ONLY on a fork PR
-    if: github.event.pull_request.head.repo.full_name != github.repository
-    name: ubuntu-latest test-py314
-    steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
-        with:
-          fetch-depth: 0
-          persist-credentials: false
-      - uses: prefix-dev/setup-pixi@f00437f565399d418b0acc85936d12c1fb668347 # v0.10.1
-        with:
-          frozen: true
-          environments: test-py314
-      - name: Check dependencies are compatible
-        run: pip check
-      - name: Run tests
-        run: pytest -n 2 --durations=10 --cov --cov-branch --cov-report=xml
-      - uses: codecov/codecov-action@fb8b3582c8e4def4969c97caa2f19720cb33a72f # v7.0.0
-        with:
-          files: ./coverage.xml