diff --git a/bugbot/rules/assignee_no_login.py b/bugbot/rules/assignee_no_login.py
index 456c49488..26aef6097 100644
--- a/bugbot/rules/assignee_no_login.py
+++ b/bugbot/rules/assignee_no_login.py
@@ -137,8 +137,8 @@ def get_priority_change_date(self, bug):
 
         for change in reversed(bug["history"]):
             if (
-                change["field_name"] == "priority"
-                and change["added"] == current_priority
+                change.get("field_name") == "priority"
+                and change.get("added") == current_priority
             ):
                 return datetime.strptime(change["when"], "%Y-%m-%dT%H:%M:%SZ")
         return None
diff --git a/tests/rules/test_assignee_no_login_priority.py b/tests/rules/test_assignee_no_login_priority.py
new file mode 100644
index 000000000..4dc3ad055
--- /dev/null
+++ b/tests/rules/test_assignee_no_login_priority.py
@@ -0,0 +1,108 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this file,
+# You can obtain one at http://mozilla.org/MPL/2.0/.
+
+"""Regression tests for the AssigneeNoLogin rule's priority-change lookup.
+
+The production fix changed ``change["field_name"]`` and ``change["added"]`` to
+``change.get("field_name")`` and ``change.get("added")`` in
+``bugbot/rules/assignee_no_login.py:get_priority_change_date``. These tests
+exercise both the pre-fix failure mode (a KeyError when history entries are
+missing one of the expected keys) and the fixed behaviour.
+"""
+
+from datetime import datetime, timezone
+
+from bugbot.rules.assignee_no_login import AssigneeNoLogin
+
+
+def _make_rule():
+    return AssigneeNoLogin(
+        username="test@example.com",
+        user_contact={"cf_id": 0, "url": "https://example.com/"},
+    )
+
+
+def test_get_priority_change_date_returns_date_when_history_entry_matches():
+    rule = _make_rule()
+    when = "2024-01-15T12:00:00Z"
+    bug = {
+        "priority": "P1",
+        "history": [
+            {"field_name": "priority", "added": "P3", "when": "2023-01-01T00:00:00Z"},
+            {"field_name": "priority", "added": "P1", "when": when},
+        ],
+    }
+
+    result = rule.get_priority_change_date(bug)
+
+    assert result == datetime(2024, 1, 15, 12, 0, 0, tzinfo=timezone.utc)
+
+
+def test_get_priority_change_date_handles_missing_field_name_without_keyerror():
+    """A history entry without ``field_name`` must not crash the lookup."""
+    rule = _make_rule()
+    when = "2024-05-20T08:30:00Z"
+    bug = {
+        "priority": "P2",
+        "history": [
+            # Missing both "field_name" and "added" - this is what crashed
+            # before the fix.
+            {"when": "2024-04-01T00:00:00Z"},
+            {"field_name": "status", "added": "NEW", "when": "2024-04-15T00:00:00Z"},
+            {"field_name": "priority", "added": "P2", "when": when},
+        ],
+    }
+
+    result = rule.get_priority_change_date(bug)
+
+    assert result == datetime(2024, 5, 20, 8, 30, 0, tzinfo=timezone.utc)
+
+
+def test_get_priority_change_date_returns_none_when_no_match():
+    rule = _make_rule()
+    bug = {
+        "priority": "P1",
+        "history": [
+            {"field_name": "priority", "added": "P2", "when": "2024-01-01T00:00:00Z"},
+            {
+                "field_name": "status",
+                "added": "RESOLVED",
+                "when": "2024-02-01T00:00:00Z",
+            },
+        ],
+    }
+
+    assert rule.get_priority_change_date(bug) is None
+
+
+def test_get_priority_change_date_skips_entries_missing_field_name():
+    """Entries that lack ``field_name`` must be skipped, not raise KeyError."""
+    rule = _make_rule()
+    bug = {
+        "priority": "P1",
+        "history": [
+            # No "field_name" key at all.
+            {"added": "P1", "when": "2024-03-10T00:00:00Z"},
+        ],
+    }
+
+    # Should not raise KeyError. The fixed implementation falls back to None
+    # when the field_name check fails (None != "priority").
+    assert rule.get_priority_change_date(bug) is None
+
+
+def test_get_priority_change_date_picks_most_recent_match():
+    rule = _make_rule()
+    bug = {
+        "priority": "P3",
+        "history": [
+            {"field_name": "priority", "added": "P1", "when": "2023-06-01T00:00:00Z"},
+            {"field_name": "priority", "added": "P2", "when": "2024-02-01T00:00:00Z"},
+            {"field_name": "priority", "added": "P3", "when": "2024-08-15T00:00:00Z"},
+        ],
+    }
+
+    result = rule.get_priority_change_date(bug)
+
+    assert result == datetime(2024, 8, 15, 0, 0, 0, tzinfo=timezone.utc)