diff --git a/.github/workflows/benchmark-diff.yml b/.github/workflows/benchmark-diff.yml
index 3adb7a9f..ff907c7c 100644
--- a/.github/workflows/benchmark-diff.yml
+++ b/.github/workflows/benchmark-diff.yml
@@ -24,7 +24,8 @@ permissions:
   pull-requests: write
 
 concurrency:
-  group: ${{ github.workflow }}-${{ github.event.pull_request.number || inputs.pr }}
+  # Keep smoke runs separate from full reruns; unrelated label events get a no-op group.
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || inputs.pr }}-${{ (github.event_name == 'workflow_dispatch' || (github.event_name == 'pull_request' && github.event.action == 'labeled' && github.event.label.name == 'rerun-benchmark')) && 'full' || (github.event_name == 'pull_request' && github.event.action != 'labeled') && 'smoke' || 'noop' }}
   cancel-in-progress: true
 
 jobs:
diff --git a/tests/test_workflow_concurrency.py b/tests/test_workflow_concurrency.py
new file mode 100644
index 00000000..acabb414
--- /dev/null
+++ b/tests/test_workflow_concurrency.py
@@ -0,0 +1,25 @@
+from pathlib import Path
+import re
+
+
+def test_benchmark_diff_separates_smoke_and_full_rerun_concurrency_groups():
+    workflow_path = Path(__file__).parents[1] / ".github/workflows/benchmark-diff.yml"
+    workflow = workflow_path.read_text(encoding="utf-8")
+    match = re.search(
+        r"(?ms)^concurrency:\n(?P<block>(?:^[ \t]+.*(?:\n|$)|^[ \t]*\n)*)",
+        workflow,
+    )
+    assert match is not None
+    concurrency = match.group("block")
+
+    group_match = re.search(r"(?m)^  group: (.+)$", concurrency)
+    assert group_match is not None
+
+    assert group_match.group(1) == (
+        "${{ github.workflow }}-${{ github.event.pull_request.number || inputs.pr }}-"
+        "${{ (github.event_name == 'workflow_dispatch' || "
+        "(github.event_name == 'pull_request' && github.event.action == 'labeled' && "
+        "github.event.label.name == 'rerun-benchmark')) && 'full' || "
+        "(github.event_name == 'pull_request' && github.event.action != 'labeled') && 'smoke' || 'noop' }}"
+    )
+    assert re.search(r"(?m)^  cancel-in-progress: true\s*$", concurrency)