diff --git a/tests/domain/epc/test_glazing_mix_guard.py b/tests/domain/epc/test_glazing_mix_guard.py
index de1faccf0..8d6e349cd 100644
--- a/tests/domain/epc/test_glazing_mix_guard.py
+++ b/tests/domain/epc/test_glazing_mix_guard.py
@@ -63,10 +63,31 @@ def test_dominant_era_stated_double_or_triple_resolves_deterministically(
     assert result is expected
 
 
+@pytest.mark.parametrize(
+    "description",
+    [
+        "95% secondary glazing (sap 9.94), 5% single glazing",
+        "90% secondary glazing, 10% double glazing 2002 or later",
+    ],
+)
+def test_dominant_secondary_glazing_resolves_to_secondary(description: str) -> None:
+    # Secondary glazing is era-free like single (SAP10 code 5, U = 2.9 regardless
+    # of install year), so a dominant-secondary split is fully determined — the
+    # guard must claim it rather than let the LLM flatten it onto the minority
+    # type (Model#1416).
+
+    # Act
+    result = glazing_mix_guard(description)
+
+    # Assert
+    assert result is GlazingType.SECONDARY
+
+
 @pytest.mark.parametrize(
     "description",
     [
         "100% double glazing 2002 or later",  # uniform — one type
+        "100% secondary glazing (sap 9.94)",  # uniform — one type
         "90% double glazing unknown age, 10% single glazing",  # dominant but era unstated
         "80% double glazing 2002 or later, 20% double glazing pre-2002",  # same base type
         "some double glazing and a bit of single",  # unparseable — no percentages