diff --git a/applications/landlord_description_overrides/handler.py b/applications/landlord_description_overrides/handler.py
index a43413b4f..dd37e461c 100644
--- a/applications/landlord_description_overrides/handler.py
+++ b/applications/landlord_description_overrides/handler.py
@@ -10,6 +10,7 @@ from applications.landlord_description_overrides.landlord_description_overrides_
 from domain.epc.property_overrides.built_form_type import BuiltFormType
 from domain.epc.property_overrides.construction_age_band import ConstructionAgeBand
 from domain.epc.property_overrides.glazing_type import GlazingType
+from domain.epc.property_overrides.glazing_mix_guard import glazing_mix_guard
 from domain.epc.property_overrides.main_fuel_type import MainFuelType
 from domain.epc.property_overrides.main_heating_system_type import MainHeatingSystemType
 from domain.epc.property_overrides.property_type import PropertyType
@@ -146,8 +147,15 @@ def _build_columns(
         "glazing": lambda src: ClassifiableColumn(
             name="glazing",
             source_column=src,
-            classifier=ChatGptColumnClassifier(
-                chat_gpt, GlazingType, GlazingType.UNKNOWN
+            # An aggregate glazing mix ("40% double, 60% single") can't be applied
+            # per-window, so the deterministic guard resolves the structured split
+            # to MIXED (no overlay → keep the cert's per-window glazing) and the LLM
+            # handles uniform / varied phrasings (#1376, ADR-0042).
+            classifier=GuardedColumnClassifier(
+                guard=glazing_mix_guard,
+                fallback=ChatGptColumnClassifier(
+                    chat_gpt, GlazingType, GlazingType.UNKNOWN
+                ),
             ),
             repo=LandlordOverridesRepository[GlazingType](
                 session, LandlordGlazingOverrideRow