diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 5f96edc07..648b5e090 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -10,7 +10,10 @@ permissions:
   contents: read
 
 concurrency:
-  group: tests-${{ github.ref }}
+  # A merged pull request can report the base ref on ``closed``. Keying PR
+  # events by number lets that close run cancel an older queued synchronize
+  # run for the same PR instead of consuming runners after the PR is closed.
+  group: tests-${{ github.event.pull_request.number || github.ref }}
   cancel-in-progress: true
 
 jobs:
diff --git a/tests/test_tests_workflow_contract.py b/tests/test_tests_workflow_contract.py
index 2fd145b0e..e6b48461a 100644
--- a/tests/test_tests_workflow_contract.py
+++ b/tests/test_tests_workflow_contract.py
@@ -1,15 +1,17 @@
-"""Regression contracts for the repository test workflow."""
+"""Regression contracts for the repository-local test workflow."""
 
 from pathlib import Path
 
 
-def test_pr_close_cancels_obsolete_test_runs_without_starting_jobs() -> None:
-    """A close event must cancel the same-PR run while scheduling no test work."""
-    workflow = (
-        Path(__file__).resolve().parents[1] / ".github/workflows/tests.yml"
-    ).read_text(encoding="utf-8")
+_WORKFLOW = Path(__file__).parents[1] / ".github" / "workflows" / "tests.yml"
+
+
+def test_pull_request_concurrency_survives_closed_ref_change() -> None:
+    """Key synchronize and closed events by PR number so close cancels stale work."""
+
+    workflow = _WORKFLOW.read_text(encoding="utf-8")
 
     assert "types: [opened, synchronize, reopened, closed]" in workflow
-    assert "group: tests-${{ github.ref }}" in workflow
+    assert "group: tests-${{ github.event.pull_request.number || github.ref }}" in workflow
     assert "cancel-in-progress: true" in workflow
     assert workflow.count("github.event.action != 'closed'") == 2