diff --git a/src/data/hours/hymn-doxology-by-feast.yml b/src/data/hours/hymn-doxology-by-feast.yml
index 7c52c38..1b1aaea 100644
--- a/src/data/hours/hymn-doxology-by-feast.yml
+++ b/src/data/hours/hymn-doxology-by-feast.yml
@@ -1,5 +1,11 @@
 # Per-feast override of the hymn's doxology stanza — real Divinum Officium
-# has a `winner{Doxology}` mechanism for this (some feasts specify their own).
-# Empty until milestone 4's sanctoral propers store exists, same as
-# prime-chapter-responsory-by-feast.yml.
-byFeastId: {}
+# has a `winner{Doxology}` mechanism for this (some feasts specify their own),
+# plus a `Rule Doxology=` mechanism a whole Common can set (e.g. the Common
+# of the BVM's own `Doxology=Nat` — Commune/C10-C12Q.txt, live-checked
+# 2026-09-03), which is why marian-saturday is keyed here by its temporal id
+# even though it's not a "feast" in the sanctoral-propers-store sense; see
+# hours/hymn-doxology.ts's getHymnDoxologyId for the kind-agnostic lookup.
+# Otherwise empty until milestone 4's sanctoral propers store exists, same
+# as prime-chapter-responsory-by-feast.yml.
+byFeastId:
+  marian-saturday: hymn-doxology-nat
diff --git a/src/hours/compline.ts b/src/hours/compline.ts
index 0054542..2d688d6 100644
--- a/src/hours/compline.ts
+++ b/src/hours/compline.ts
@@ -30,9 +30,7 @@ function resolvePart(part: HourPart, day: LiturgicalDay): ResolvedPart[] {
         return [{ kind: 'hymn', text: resolveCommon('compline-hymn-lenten') }];
       }
       const body = resolveCommon(part.textRef.id);
-      const doxology = resolveCommon(
-        getHymnDoxologyId(day.season, day.winner, 'compline-hymn-doxology-per-annum'),
-      );
+      const doxology = resolveCommon(getHymnDoxologyId(day, 'compline-hymn-doxology-per-annum'));
       return [{ kind: 'hymn', text: appendDoxology(body, doxology) }];
     }
     case 'chapter':
diff --git a/src/hours/hymn-doxology.ts b/src/hours/hymn-doxology.ts
index d685117..cc32afc 100644
--- a/src/hours/hymn-doxology.ts
+++ b/src/hours/hymn-doxology.ts
@@ -1,21 +1,55 @@
-import type { Season, DayWinner } from '../calendar/types';
-import { resolveSeasonalPropersId } from './seasonal-propers';
+import type { LiturgicalDay } from '../calendar/types';
+import { resolveOfficeWinner } from './resolve-common';
 import bySeasonData from '../data/hours/hymn-doxology-by-season.yml';
 import byFeastData from '../data/hours/hymn-doxology-by-feast.yml';
 
 const bySeason = bySeasonData as { bySeason: Record<string, string> };
 const byFeast = byFeastData as { byFeastId: Record<string, string> };
 
+const NAT_DOXOLOGY_ID = 'hymn-doxology-nat';
+
+/**
+ * Divinum Officium's own doxology() sub (specials/hymni.pl) hardcodes the
+ * Assumption's octave (Aug 16-22) to the Nativity doxology, regardless of
+ * season or which feast is winning that day — live-checked in the source,
+ * and *not* excluded for the Monastic/Tridentine 1617 track (unlike its
+ * Dec 9-15 companion rule for the Immaculate Conception's run-up, which the
+ * source explicitly excludes 1570/1617/1963/altovadensis from, so that one
+ * is deliberately NOT ported here). Checked directly by date, same pattern
+ * as marian-antiphon.ts's isCandlemasToHolyWednesday — this window doesn't
+ * line up with any `Season` value.
+ */
+function isAssumptionOctaveWindow(isoDate: string): boolean {
+  const [, monthStr, dayStr] = isoDate.split('-');
+  const month = Number(monthStr);
+  const day = Number(dayStr);
+  return month === 8 && day > 15 && day < 23;
+}
+
 /**
  * Resolves the common-propers id for a hymn's seasonal final doxology
  * stanza. The seasonal overrides are shared across every hymn (Divinum
  * Officium's own Doxologies.txt table is hymn-agnostic), but the per-annum
  * default is each hymn's own natural ending, so callers supply it.
+ *
+ * Precedence, matching hymni.pl's doxology() sub: (1) an explicit per-feast
+ * override — real Divinum Officium's `winner{Doxology}`/`Rule Doxology=`
+ * mechanism, e.g. the Common of the BVM's own `Doxology=Nat` rule, which is
+ * why Marian Saturdays (a `kind: 'temporal'` winner, not `'sanctoral'` —
+ * checked regardless of kind, unlike chapter-responsory's/opening-
+ * versicle's own byFeastId tables, since a temporal id and a sanctoral id
+ * never collide) get the Nativity doxology even outside Christmastide; (2)
+ * the Assumption-octave date window above; (3) the season; (4) the hymn's
+ * own per-annum default.
  */
-export function getHymnDoxologyId(season: Season, winner: DayWinner, perAnnumId: string): string {
-  return resolveSeasonalPropersId(season, winner, {
-    perAnnum: perAnnumId,
-    bySeason: bySeason.bySeason,
-    byFeastId: byFeast.byFeastId,
-  });
+export function getHymnDoxologyId(day: LiturgicalDay, perAnnumId: string): string {
+  const winner = resolveOfficeWinner(day);
+  const feastOverride = winner.kind === 'sanctoral' || winner.kind === 'temporal' ? byFeast.byFeastId[winner.id] : undefined;
+  if (feastOverride) {
+    return feastOverride;
+  }
+  if (isAssumptionOctaveWindow(day.date)) {
+    return NAT_DOXOLOGY_ID;
+  }
+  return bySeason.bySeason[day.season] ?? perAnnumId;
 }
diff --git a/src/hours/prime.ts b/src/hours/prime.ts
index 0e4dece..b462b60 100644
--- a/src/hours/prime.ts
+++ b/src/hours/prime.ts
@@ -30,7 +30,7 @@ function resolvePart(part: HourPart, date: string, day: LiturgicalDay): Resolved
   switch (part.kind) {
     case 'hymn': {
       const body = resolveCommon(part.textRef.id);
-      const doxology = resolveCommon(getHymnDoxologyId(day.season, day.winner, 'hymn-doxology-per-annum'));
+      const doxology = resolveCommon(getHymnDoxologyId(day, 'hymn-doxology-per-annum'));
       return [{ kind: 'hymn', text: appendDoxology(body, doxology) }];
     }
     case 'chapter':