diff --git a/docs/decisions/0005-issues-own-tracker-metadata.md b/docs/decisions/0005-issues-own-tracker-metadata.md
index 98acbc0d..43f3e956 100644
--- a/docs/decisions/0005-issues-own-tracker-metadata.md
+++ b/docs/decisions/0005-issues-own-tracker-metadata.md
@@ -29,7 +29,8 @@ item exists. Every issue has at least one label. An issue opened or left
 without labels receives `Status/Needs Triage` automatically until it is
 classified.
 
-Every new pull request is tracked in one of two ways:
+Every new pull request is tracked in exactly one of two mutually exclusive
+ways:
 
 1. It deliberately references at least one existing issue in its title or
    description. Tracker metadata stays on that issue and the PR remains
@@ -43,9 +44,9 @@ Issue references use one of these forms:
 - `Part of #123`, `Related to #123`, `Refs #123`, or `References #123` when it
   contributes without completing it.
 
-Gitea Actions enforces the either/or PR rule, validates any issue references,
-and repairs the empty issue-label state. Branch protection makes the PR policy
-check required.
+Gitea Actions enforces the exclusive either/or PR rule, validates any issue
+references, and repairs the empty issue-label state. Branch protection makes
+the PR policy check required.
 
 The policy applies from 2026-07-18 onward. Existing issues may be labelled as
 they are encountered, but closed PRs are grandfathered: no retrospective
@@ -70,5 +71,6 @@ issues or PR labels are created solely to make history conform.
 ## Links
 
 - Issue #405.
-- `.gitea/workflows/tracker-policy.yml`.
+- `.gitea/workflows/tracker-policy-pr.yml`.
+- `.gitea/workflows/tracker-policy-issues.yml`.
 - `scripts/tracker_policy.py`.
diff --git a/scripts/tracker_policy.py b/scripts/tracker_policy.py
index aec64a24..144aa27a 100644
--- a/scripts/tracker_policy.py
+++ b/scripts/tracker_policy.py
@@ -55,6 +55,12 @@ def check_pull_request(event: dict[str, Any], api: GiteaApi) -> list[str]:
     errors: list[str] = []
     labels = pull.get("labels") or []
     numbers = deliberate_issue_numbers(pull.get("title", ""), pull.get("body", ""))
+    if labels and numbers:
+        errors.append(
+            "PR must use exactly one tracking mode: remove PR labels when "
+            "linking an issue, or remove the issue reference when labels "
+            "belong on the PR."
+        )
     if not numbers:
         if not labels:
             errors.append(
diff --git a/tests/unit/test_tracker_policy.py b/tests/unit/test_tracker_policy.py
index 517d33ce..3dba3c3a 100644
--- a/tests/unit/test_tracker_policy.py
+++ b/tests/unit/test_tracker_policy.py
@@ -47,7 +47,21 @@ class TestCheckPullRequest(unittest.TestCase):
         self.assertIn("either have a label or reference an issue", errors[0])
         api.request.assert_not_called()
 
-    def test_validates_issue_reference_even_when_pr_is_labelled(self):
+    def test_rejects_labelled_pr_linked_to_real_issue(self):
+        api = Mock()
+        api.request.return_value = {"number": 12, "pull_request": None}
+        event = {
+            "pull_request": {
+                "title": "Change",
+                "body": "Closes #12",
+                "labels": [{"name": "Kind/Documentation"}],
+            }
+        }
+        errors = check_pull_request(event, api)
+        self.assertEqual(len(errors), 1)
+        self.assertIn("exactly one tracking mode", errors[0])
+
+    def test_still_validates_issue_reference_when_both_modes_are_used(self):
         api = Mock()
         api.request.return_value = {"number": 12, "pull_request": {}}
         event = {
@@ -58,8 +72,9 @@ class TestCheckPullRequest(unittest.TestCase):
             }
         }
         errors = check_pull_request(event, api)
-        self.assertEqual(len(errors), 1)
-        self.assertIn("not an issue", errors[0])
+        self.assertEqual(len(errors), 2)
+        self.assertIn("exactly one tracking mode", errors[0])
+        self.assertIn("not an issue", errors[1])
 
 
 class TestEnsureIssueLabel(unittest.TestCase):