diff --git a/etl/hubspot/tests/test_abri_flow_triggers.py b/etl/hubspot/tests/test_abri_flow_triggers.py
index d8bbfb668..77aa04daf 100644
--- a/etl/hubspot/tests/test_abri_flow_triggers.py
+++ b/etl/hubspot/tests/test_abri_flow_triggers.py
@@ -227,6 +227,64 @@ def test_the_message_carries_the_deals_third_party_surveyor_identifier() -> None
     assert message["third_party_surveyor_identifier"] == "THIRDPARTY"
 
 
+def test_the_message_carries_the_deals_client_booking_reference() -> None:
+    # Arrange: an amend on a deal that already carries a Job Number; the
+    # consumer reads the reference off the message to decide the job exists.
+    old_deal = make_old_deal(
+        project_code=ABRI_PROJECT_CODE,
+        confirmed_survey_date=datetime(2026, 6, 18, tzinfo=timezone.utc),
+        third_party_surveyor_identifier="THIRDPARTY",
+        client_booking_reference="AD0226519",
+    )
+    new_deal = make_new_deal(
+        confirmed_survey_date="2026-06-24",
+        confirmed_survey_time="14:30",
+        third_party_surveyor_identifier="THIRDPARTY",
+        client_booking_reference="AD0226519",
+    )
+
+    # Act
+    message = HubspotDealDiffer.check_abri_triggers_and_construct_message(
+        hubspot_deal_id=DEAL_ID,
+        new_deal=new_deal,
+        new_project=None,
+        new_listing=LISTING,
+        old_deal=old_deal,
+    )
+
+    # Assert
+    assert message is not None
+    assert message["flows"] == ["amend_job"]
+    assert message["client_booking_reference"] == "AD0226519"
+
+
+def test_the_message_omits_the_client_booking_reference_when_the_deal_has_none() -> None:
+    # Arrange: a pair-completing log on a deal with no Job Number yet.
+    old_deal = make_old_deal(
+        project_code=ABRI_PROJECT_CODE,
+        confirmed_survey_date=None,
+        third_party_surveyor_identifier=None,
+    )
+    new_deal = make_new_deal(
+        confirmed_survey_date="2026-06-24",
+        confirmed_survey_time="14:30",
+        third_party_surveyor_identifier="THIRDPARTY",
+    )
+
+    # Act
+    message = HubspotDealDiffer.check_abri_triggers_and_construct_message(
+        hubspot_deal_id=DEAL_ID,
+        new_deal=new_deal,
+        new_project=None,
+        new_listing=LISTING,
+        old_deal=old_deal,
+    )
+
+    # Assert
+    assert message is not None
+    assert message["client_booking_reference"] is None
+
+
 def test_a_changed_survey_date_on_a_complete_booking_builds_an_amend_job_message() -> None:
     # Arrange: a complete booking (date + surveyor) whose date moves.
     old_deal = make_old_deal(