diff --git a/domain/epc/property_overrides/glazing_mix_guard.py b/domain/epc/property_overrides/glazing_mix_guard.py
index 5d59e4fa1..05b0fb2b0 100644
--- a/domain/epc/property_overrides/glazing_mix_guard.py
+++ b/domain/epc/property_overrides/glazing_mix_guard.py
@@ -17,11 +17,12 @@ _PERCENT_TYPE = re.compile(
 # One base type at or above this share is a uniform assertion, not a mix — applied
 # as that type (a near-uniform reglaze), not deferred.
 _UNIFORM_THRESHOLD_PERCENT = 90
-# A dominant base type + stated era → the fully-determined canonical member. Single
-# glazing is era-free, so it needs no era. Double/triple with no (or non-canonical)
-# era is absent here and falls through to the LLM.
+# A dominant base type + stated era → the fully-determined canonical member.
+# Single and secondary glazing are era-free, so they need no era. Double/triple
+# with no (or non-canonical) era is absent here and falls through to the LLM.
 _DOMINANT_MEMBER: dict[tuple[str, Optional[str]], GlazingType] = {
     ("single", None): GlazingType.SINGLE,
+    ("secondary", None): GlazingType.SECONDARY,
     ("double", "2002 or later"): GlazingType.DOUBLE_POST_2002,
     ("double", "pre-2002"): GlazingType.DOUBLE_PRE_2002,
     ("triple", "2002 or later"): GlazingType.TRIPLE_POST_2002,
@@ -51,9 +52,9 @@ def glazing_mix_guard(description: str) -> Optional[GlazingType]:
     * ``MIXED`` for a genuine mix — two or more glazing types present and none
       dominant (≥ the uniform threshold);
     * the fully-determined member for a dominant near-uniform split whose type
-      carries no era ambiguity — single glazing (era-free), or a dominant
-      double/triple whose era is stated ("pre-2002" / "2002 or later"); the LLM
-      would otherwise flatten such a split onto its *minority* type;
+      carries no era ambiguity — single or secondary glazing (era-free), or a
+      dominant double/triple whose era is stated ("pre-2002" / "2002 or later");
+      the LLM would otherwise flatten such a split onto its *minority* type;
     * ``None`` otherwise — an unparseable description, or a dominant double/triple
       with an unstated/non-canonical era ("unknown age") that still carries genuine
       era ambiguity — so the LLM classifier resolves it.