diff --git a/TODO.md b/TODO.md
index ac53332..a70c594 100644
--- a/TODO.md
+++ b/TODO.md
@@ -2296,6 +2296,38 @@ two years' Easter dates, and `tests/calendar/august-sanctoral.test.ts`'s existin
 was updated to match (the day now reverts to the plain Assumption octave, same shape as St.
 Lawrence's own Aug 12 case). `npm test` (429 tests) and `tsc --noEmit` both pass.
 
+### Assumption-octave Matins hymn fixed (2026-08-22)
+
+Separately, the "no antiphons and a weird hymn today" complaint that prompted the investigation
+above turned out to be a distinct, narrower bug: `resolveMatinsHymn`'s own doc comment
+already claimed the Assumption's octave "keeps the feast's own proper hymn all week," but the
+code never implemented that — it only fired when the day's own winner literally *was*
+`assumption` (Aug 15 only). Every other octave day (16, 17, 19, 20, 21 — St. Joachim, St.
+Hyacinth, St. John Eudes, St. Bernard, St. Jane Frances de Chantal, none of whom has a Matins
+hymn of their own authored) fell straight to the plain ferial hymn. Fixed by adding a real
+octave-fallback tier (`resolveActiveOctave(day.date)` → `matins-hymn-${octave.id}`) between the
+existing per-feast override and the seasonal tier. Confirmed against the reference engine that
+Monastic 1617 itself doesn't do this either (no octave day there has its own `[Hymnus
+Matutinum]` override) — this is a deliberate departure, not a restoration, consistent with how
+this project already treats octave readings/commemorations more generously than any one source
+track. Aug 18 (no sanctoral winner) and Aug 22 (once IHM moved) needed no change — both already
+reached `matins-hymn-assumption` via the pre-existing `resolveOfficeWinner` octave-substitution
+path, which only fires when the day's own winner isn't sanctoral.
+
+**Not fixed, logged instead** (user decision): the deeper reason Matins had *zero* nocturn
+antiphons at all on Aug 22 — no `matins-psalmody-overrides` entry exists for `assumption` or
+`immaculate-heart-of-mary` (or, generally, any Duplex-2-classis+ feast lacking one), so Matins
+falls all the way to the bare ferial psalm table, which by design carries no antiphons — is a
+broader content gap than today's date, tracked in the "Matins psalmody overrides" bullet above
+rather than authored now. Also newly true because of this change: `hours/matins.ts`'s psalmody
+override lookup is hard-gated to `winner.kind === 'sanctoral'`, so even if IHM's psalmody were
+authored later, it wouldn't apply as a temporal-kind winner without that gate being loosened
+too — noted for whoever picks this up.
+
+New tests in `tests/hours/matins.test.ts` cover the fallback across Aug 16-22, including the
+Aug 17 edge case (correctly still ferial, since that day is actually governed by St. Lawrence's
+own octave, not the Assumption's). `npm test` (430 tests) and `tsc --noEmit` both pass.
+
 ## Known, deliberate simplifications (not bugs — working as designed)
 
 - `getDayCollects`: each collect in a multi-collect day renders as its own
diff --git a/src/hours/matins.ts b/src/hours/matins.ts
index bb39f9c..270fe4d 100644
--- a/src/hours/matins.ts
+++ b/src/hours/matins.ts
@@ -62,7 +62,7 @@
 // full-calendar content pass. See TODO.md for what's deferred.
 import type { ResolvedOrdo, ResolvedPart, ResolvedText, ResolvedVerse } from './types';
 import type { LiturgicalDay } from '../calendar/types';
-import { resolveDay, resolveTemporalId, activeOctavesFor } from '../calendar';
+import { resolveDay, resolveTemporalId, activeOctavesFor, resolveActiveOctave } from '../calendar';
 import { isInTriduum } from '../calendar/temporal';
 import { getDayLabel } from '../calendar/day-label';
 import { getPsalmVerses } from '../psalter';
@@ -215,14 +215,28 @@ function sundayCanticleNocturn(group: SundayNocturn, day: LiturgicalDay): Resolv
 /** The Matins hymn — a duplex-majus+ saint's or eligible named temporal
  * feast's own proper hymn (`matins-hymn-${overrideId}`, via the same
  * getOfficeOverrideId eligibility Lauds/Vespers' own resolveOffice uses),
- * when authored, else falls to a *seasonal* default (Advent/Lent/
+ * when authored; else, on a day within an active octave whose own feast
+ * has a hymn authored, that octave's hymn (`matins-hymn-${octave.id}`) —
+ * see below; else falls to a *seasonal* default (Advent/Lent/
  * Passiontide/Paschaltide, none authored yet), else the plain year-round
- * ferial hymn — same override > season > ferial precedence every other
- * hour's own office bundle uses (see lauds.ts's resolveOffice), just never
- * wired up here before. Concrete motivating case (user, 2026-08-21): the
- * Assumption's octave (`Sancti/08-21bmv.txt`'s own `[Rule] ex Sancti/
- * 08-15`) genuinely keeps the feast's own proper hymn all week, not the
- * ferial one this always rendered previously. */
+ * ferial hymn — same override > octave > season > ferial precedence every
+ * other hour's own office bundle uses (see lauds.ts's resolveOffice), just
+ * never fully wired up here before.
+ *
+ * Concrete motivating case (user, 2026-08-21/22): the Assumption's octave
+ * (`Sancti/08-21bmv.txt`'s own `[Rule] ex Sancti/08-15`) genuinely keeps
+ * the feast's own proper hymn all week — a claim this comment already
+ * made before the octave tier below actually existed, which only ever
+ * fired on Aug 15 itself (the one day `overrideId` literally *is*
+ * `assumption`). Every other octave day (16, 17, 19, 20, 21, each with
+ * its own named saint who has no Matins hymn of their own authored) fell
+ * straight through to the plain ferial hymn instead. This is a deliberate
+ * departure from the reference engine, which doesn't do this either
+ * (Monastic 1617's own octave days have no `[Hymnus Matutinum]` override
+ * at all, live-checked 2026-08-22) — not a restoration of source
+ * behavior, just this project's own generous octave design (see
+ * "Not a reconstruction" in the repo's CLAUDE.md) applied to the hymn the
+ * same way it's already applied to readings/commemorations elsewhere. */
 function resolveMatinsHymn(day: LiturgicalDay): ResolvedText {
   const overrideId = getOfficeOverrideId(day);
   if (overrideId) {
@@ -231,6 +245,13 @@ function resolveMatinsHymn(day: LiturgicalDay): ResolvedText {
       return proper;
     }
   }
+  const octave = resolveActiveOctave(day.date);
+  if (octave) {
+    const octaveHymn = resolveCommon(`matins-hymn-${octave.id}`);
+    if (octaveHymn.status.la !== 'missing' || octaveHymn.status.en !== 'missing') {
+      return octaveHymn;
+    }
+  }
   const seasonSuffix = seasonalOfficeSuffix(day.season);
   if (seasonSuffix) {
     const seasonal = resolveCommon(`matins-hymn-${seasonSuffix}`);
diff --git a/tests/hours/matins.test.ts b/tests/hours/matins.test.ts
index 2829913..b3ba122 100644
--- a/tests/hours/matins.test.ts
+++ b/tests/hours/matins.test.ts
@@ -371,3 +371,39 @@ describe('resolveOrdo("matins", ...) Sacred Triduum', () => {
     expect(ordo.parts[1]).toMatchObject({ kind: 'psalm', psalmNumber: 3 });
   });
 });
+
+describe('resolveOrdo("matins", ...) Assumption-octave hymn fallback (2026-08-22 fix)', () => {
+  // Real bug: resolveMatinsHymn's own doc comment already claimed the
+  // Assumption's octave "keeps the feast's own proper hymn all week," but
+  // the code only ever matched when the day's own winner literally *was*
+  // `assumption` (Aug 15 itself) -- every other octave day fell straight
+  // through to the plain ferial hymn instead. Fixed by adding a real
+  // octave-fallback tier (resolveActiveOctave -> `matins-hymn-${octave.id}`).
+  function hymnLatin(date: string): string | undefined {
+    const ordo = resolveOrdo('matins', date);
+    const hymn = ordo.parts.find((p) => p.kind === 'hymn') as { text: { text: { la: string } } } | undefined;
+    return hymn?.text.text.la;
+  }
+
+  it("St. Bernard's own day (Aug 20, no hymn of his own authored) picks up the Assumption's octave hymn, not the plain ferial one", () => {
+    expect(hymnLatin('2026-08-20')).toContain('Surge');
+  });
+
+  it('every other interior day governed by the Assumption octave (16, 19, 21 — none with a hymn of their own) also picks up the octave hymn', () => {
+    for (const date of ['2026-08-16', '2026-08-19', '2026-08-21']) {
+      expect(hymnLatin(date)).toContain('Surge');
+    }
+  });
+
+  it("Aug 17 is instead governed by St. Lawrence's own octave (its own elevated closing day, outranking the Assumption's ordinary day here) — no hymn authored for it, so it still falls to the plain ferial one, correctly", () => {
+    expect(hymnLatin('2026-08-17')).toContain('Somno');
+  });
+
+  it('Aug 22, the octave-closing day (Immaculate Heart of Mary relocated away), also gets the Assumption hymn via the pre-existing sanctoral-substitution path', () => {
+    expect(hymnLatin('2026-08-22')).toContain('Surge');
+  });
+
+  it("a plain ferial day outside the octave still gets the plain ferial hymn, unaffected", () => {
+    expect(hymnLatin(FERIAL_DATE)).toContain('Somno');
+  });
+});