diff --git a/src/data/propers/common/matins-hymn-common-of-an-apostle.yml b/src/data/propers/common/matins-hymn-common-of-an-apostle.yml
new file mode 100644
index 0000000..63e0048
--- /dev/null
+++ b/src/data/propers/common/matins-hymn-common-of-an-apostle.yml
@@ -0,0 +1,101 @@
+# The Common-of-an-Apostle's own Matins hymn ("Ætérna Christi múnera" /
+# "Th' eternal gifts of Christ the King"), read from the reference engine's
+# own Commune/C1.txt [Hymnus Matutinum] block (both Latin and English
+# present and complete there). Any winning apostle with no proper Matins
+# hymn of his own authored falls to this Common tier (hours/matins.ts's
+# resolveMatinsHymn) — e.g. St. Bartholomew (2026-08-24, live-verified):
+# Monastic 1617 gives him no [Hymnus Matutinum] override of his own, so
+# this Common's own text genuinely renders.
+id: matins-hymn-common-of-an-apostle
+text:
+  la: >-
+    Ætérna Christi múnera,
+
+    Apostolórum glóriam,
+
+    Palmas et hymnos débitos
+
+    Lætis canámus méntibus.
+
+
+    Ecclesiárum Príncipes,
+
+    Belli triumpháles duces,
+
+    Cæléstis aulæ mílites,
+
+    Et vera mundi lúmina.
+
+
+    Devóta Sanctórum fides,
+
+    Invícta spes credéntium,
+
+    Perfécta Christi cáritas
+
+    Mundi tyránnum cónterit.
+
+
+    In his Patérna glória,
+
+    In his triúmphat Fílius,
+
+    In his volúntas Spíritus,
+
+    Cælum replétur gáudio.
+
+
+    Patri, simúlque Fílio,
+
+    Tibíque Sancte Spíritus,
+
+    Sicut fuit, sit júgiter
+
+    Sæclum per omne glória. Amen.
+  en: >-
+    Th' eternal gifts of Christ the King,
+
+    The Apostles' glory, let us sing;
+
+    And all with hearts of gladness raise
+
+    Due hymns of thankful love and praise.
+
+
+    For they the Church's princes are,
+
+    Triumphant leaders in the war,
+
+    The heavenly King's own warrior band,
+
+    True lights to lighten every land.
+
+
+    Theirs was the steadfast faith of saints,
+
+    The hope that never yields nor faints,
+
+    The love of Christ in perfect glow,
+
+    That lay the prince of this world low.
+
+
+    In them the Father's glory shone,
+
+    In them the Spirit's will was done,
+
+    The Son himself exults in them;
+
+    Joy fills the new Jerusalem.
+
+
+    Praise to the Father, with the Son,
+
+    And Holy Spirit, Three in One;
+
+    As ever was in ages past,
+
+    And so shall be while ages last. Amen.
+status:
+  la: verified
+  en: verified
diff --git a/src/data/propers/common/matins-invitatory-common-of-an-apostle.yml b/src/data/propers/common/matins-invitatory-common-of-an-apostle.yml
new file mode 100644
index 0000000..e5543a5
--- /dev/null
+++ b/src/data/propers/common/matins-invitatory-common-of-an-apostle.yml
@@ -0,0 +1,13 @@
+# The Common-of-an-Apostle's own invitatory antiphon ("Regem Apostolórum
+# Dóminum" / "The Lord, the King of Apostles"), read from the reference
+# engine's own Commune/C1.txt [Invit] line (both languages). Any winning
+# apostle with no proper invitatory antiphon of his own authored falls to
+# this Common tier (hours/matins.ts's resolveMatinsInvitatoryText) — e.g.
+# St. Bartholomew (2026-08-24, live-verified).
+id: matins-invitatory-common-of-an-apostle
+text:
+  la: "Regem Apostolórum Dóminum, * Veníte, adorémus."
+  en: "The Lord, the King of Apostles, * O come, let us adore."
+status:
+  la: verified
+  en: verified
diff --git a/src/hours/matins.ts b/src/hours/matins.ts
index 4c3f114..29de2ba 100644
--- a/src/hours/matins.ts
+++ b/src/hours/matins.ts
@@ -80,6 +80,7 @@ import {
   splitNamedAntiphon,
   openingAntiphon,
 } from './resolve-common';
+import { getSaintRecord } from '../calendar/feasts';
 import { getBiblePlanReadings } from '../propers/bible-plan';
 import { getNocturnReadings, type NocturnReading } from '../propers/nocturn-readings';
 import { getOctaveReading } from '../propers/octave-readings';
@@ -168,14 +169,56 @@ function psalmRefParts(refs: PsalmRef[]): ResolvedPart[] {
   }));
 }
 
+/** The invitatory antiphon's own text — same override > Common-category >
+ * seasonal > ferial precedence as `resolveMatinsHymn`, minus the octave
+ * tier: no per-octave invitatory-antiphon override exists anywhere in the
+ * reference source (unlike the hymn, which genuinely persists all week on
+ * some octaves) — an octave day already falls through correctly to its
+ * governing saint's own Common/season tier here, so adding an octave tier
+ * would have nothing to fire on. Keeps the existing ferial fallback id
+ * (`matins-invitatory-antiphon`) as-is rather than renaming it to match
+ * the hymn's `-ferial` convention — it's already `verified` and its own
+ * header already documents itself as the fallback-of-record; renaming
+ * would be pure churn.
+ *
+ * Doubling (`isDoubleOrHigher`, via `openingAntiphon`) is a separate, final
+ * step applied to whichever tier's text wins here — never part of content
+ * selection itself. */
+function resolveMatinsInvitatoryText(day: LiturgicalDay): ResolvedText {
+  const overrideId = getOfficeOverrideId(day);
+  if (overrideId) {
+    const proper = resolveCommon(`matins-invitatory-${overrideId}`);
+    if (proper.status.la !== 'missing' || proper.status.en !== 'missing') {
+      return proper;
+    }
+  }
+  const winner = resolveOfficeWinner(day);
+  const commonId = winner.kind === 'sanctoral' ? getSaintRecord(winner.id)?.common : undefined;
+  if (commonId) {
+    const common = resolveCommon(`matins-invitatory-${commonId}`);
+    if (common.status.la !== 'missing' || common.status.en !== 'missing') {
+      return common;
+    }
+  }
+  const seasonSuffix = seasonalOfficeSuffix(day.season);
+  if (seasonSuffix) {
+    const seasonal = resolveCommon(`matins-invitatory-${seasonSuffix}`);
+    if (seasonal.status.la !== 'missing' || seasonal.status.en !== 'missing') {
+      return seasonal;
+    }
+  }
+  return resolveCommon('matins-invitatory-antiphon');
+}
+
 /** The Invitatory (Ps 94) — real practice interleaves its antiphon as a
  * repeating refrain between verse groups; per direct instruction this app
  * frames it like any other psalm antiphon instead (one opening, one full
  * repeat after) — see data/propers/common/matins-invitatory-antiphon.yml's
  * own header. */
 function invitatoryParts(day: LiturgicalDay): ResolvedPart[] {
-  const { incipit, full } = splitNamedAntiphon(resolveCommon('matins-invitatory-antiphon'));
-  const opening = isDoubleOrHigher(resolveOfficeWinner(day)) ? full : incipit;
+  const text = resolveMatinsInvitatoryText(day);
+  const opening = openingAntiphon(text, resolveOfficeWinner(day));
+  const { full } = splitNamedAntiphon(text);
   return [
     psalmPartWithAntiphon(94, opening),
     { kind: 'antiphon', text: full },
@@ -229,11 +272,16 @@ function sundayCanticleNocturn(group: SundayNocturn, day: LiturgicalDay): Resolv
  * getOfficeOverrideId eligibility Lauds/Vespers' own resolveOffice uses),
  * when authored; else, on a day within an active octave whose own feast
  * has a hymn authored, that octave's hymn (`matins-hymn-${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 > octave > season > ferial precedence every
- * other hour's own office bundle uses (see lauds.ts's resolveOffice), just
- * never fully wired up here before.
+ * see below; else the winner's Common-of-Saints hymn (`matins-hymn-
+ * ${commonId}`, via `SaintRecord.common`, e.g. "Aeterna Christi munera"
+ * for any Apostle with no proper hymn of his own — same category-lookup
+ * pattern as matins-psalmody-overrides.ts's getMatinsPsalmodyOverride);
+ * else falls to a *seasonal* default (Advent/Lent/Passiontide/
+ * Paschaltide, none authored yet), else the plain year-round ferial hymn —
+ * override > octave > Common > season > ferial. Common slots between
+ * octave and season: an octave's own proper hymn is more specific than any
+ * Common and must keep winning; a Common-of-Saints hymn is more specific
+ * than a bare season and must win over it.
  *
  * Concrete motivating case (user, 2026-08-21/22): the Assumption's octave
  * (`Sancti/08-21bmv.txt`'s own `[Rule] ex Sancti/08-15`) genuinely keeps
@@ -264,6 +312,23 @@ function resolveMatinsHymn(day: LiturgicalDay): ResolvedText {
       return octaveHymn;
     }
   }
+  // Common-of-Saints tier (2026-08): a winning saint with no proper hymn of
+  // his own (most of them) still often shares a real, generic hymn with
+  // every other saint of his Common (e.g. "Aeterna Christi munera" for any
+  // Apostle) — same getSaintRecord(id)?.common lookup already proven by
+  // matins-psalmody-overrides.ts's getMatinsPsalmodyOverride. Keyed off the
+  // actual winner, not `overrideId` above: `getOfficeOverrideId` only
+  // returns an id for duplex-majus+ winners (an eligibility gate for the
+  // per-saint-proper tier), so reusing it here would silently skip this
+  // tier for any lower-ranked sanctoral winner.
+  const winner = resolveOfficeWinner(day);
+  const commonId = winner.kind === 'sanctoral' ? getSaintRecord(winner.id)?.common : undefined;
+  if (commonId) {
+    const commonHymn = resolveCommon(`matins-hymn-${commonId}`);
+    if (commonHymn.status.la !== 'missing' || commonHymn.status.en !== 'missing') {
+      return commonHymn;
+    }
+  }
   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 4f6cc41..5416658 100644
--- a/tests/hours/matins.test.ts
+++ b/tests/hours/matins.test.ts
@@ -525,3 +525,76 @@ describe('resolveOrdo("matins", ...) nocturn-reading temporal/month-week suppres
     const lessons = ordo.parts.filter((p) => p.kind === 'lesson') as { text: { status: Record<string, string> } }[];
     expect(lessons.length).toBeGreaterThan(0);
     expect(lessons.some((l) => l.text.status.la !== 'missing' && l.text.status.en !== 'missing')).toBe(true);
+  });
+});
+
+// Coverage gap fix (no bug found): the pre-existing ferial-branch test
+// above only asserted the opening invitatory antiphon *contains* "Veníte,"
+// true for both the incipit ("Ant. Veníte.") and full ("Ant. Veníte, *
+// Exsultémus Dómino.") forms -- it never actually distinguished doubled vs.
+// undoubled. isDoubleOrHigher/openingAntiphon traced out correct in source
+// for every rank tested here; these tests just make the distinction real.
+describe('resolveOrdo("matins", ...) invitatory antiphon doubling by rank', () => {
+  function openingAntiphonLatin(date: string): string | undefined {
+    const ordo = resolveOrdo('matins', date);
+    const invitatoryPsalm = ordo.parts.find((p) => p.kind === 'psalm' && (p as { psalmNumber: number }).psalmNumber === 94) as
+      | { antiphon?: { text: Record<string, string> } }
+      | undefined;
+    return invitatoryPsalm?.antiphon?.text.la;
+  }
+
+  it('a Duplex+ weekday winner opens with the FULL (not incipit-only) invitatory antiphon (St. Lawrence, 2026-08-17: ferial text, no proper/Common of his own; St. Bartholomew, duplex-2-classis, 2026-08-24: Common-of-an-Apostle text)', () => {
+    expect(openingAntiphonLatin('2026-08-17')).toContain('Exsultémus');
+    expect(openingAntiphonLatin('2026-08-24')).toContain('Regem Apostolórum Dóminum, * Veníte');
+  });
+
+  it('a plain ferial day opens with the incipit only', () => {
+    expect(openingAntiphonLatin(FERIAL_DATE)).not.toContain('Exsultémus');
+  });
+
+  it("a Simplex saint merely commemorated (not winning) under an Advent feria still opens with the incipit only — the winner's own rank governs, not any commemorated saint's (St. Bibiana, 2025-12-02)", () => {
+    expect(openingAntiphonLatin('2025-12-02')).not.toContain('Exsultémus');
+  });
+});
+
+// New mechanism (2026-08): resolveMatinsHymn gained a Common-of-Saints
+// tier (override -> octave -> Common category -> season -> ferial), and
+// the invitatory antiphon -- previously one hardcoded fixed text for every
+// day of the year -- now goes through the same shape of tiering
+// (resolveMatinsInvitatoryText: override -> Common category -> season ->
+// ferial). Both confirmed against the reference engine's own Commune/
+// C1.txt (Common of an Apostle): hymn "Ætérna Christi múnera," invitatory
+// "Regem Apostolórum Dóminum." St. Bartholomew has no proper Matins hymn
+// or invitatory of his own authored, so this Common tier is what actually
+// renders for him.
+describe('resolveOrdo("matins", ...) Common-of-an-Apostle hymn + invitatory (2026-08-24 fix)', () => {
+  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;
+  }
+  function invitatoryFullLatin(date: string): string | undefined {
+    const ordo = resolveOrdo('matins', date);
+    const antiphonParts = ordo.parts.filter((p) => p.kind === 'antiphon') as { text: { text: Record<string, string> } }[];
+    return antiphonParts[0]?.text.text.la;
+  }
+
+  it("St. Bartholomew's own day (2026-08-24, no proper Matins hymn of his own) picks up the Common-of-an-Apostle hymn", () => {
+    expect(hymnLatin('2026-08-24')).toContain('Ætérna Christi múnera');
+  });
+
+  it("St. Bartholomew's invitatory antiphon resolves to the Common-of-an-Apostle text", () => {
+    expect(invitatoryFullLatin('2026-08-24')).toContain('Regem Apostolórum Dóminum');
+  });
+
+  it('St. Andrew (2026-11-30, also common-of-an-apostle, no proper hymn/invitatory of his own) resolves to the same Common text -- confirms the tier generalizes beyond Bartholomew', () => {
+    expect(hymnLatin('2026-11-30')).toContain('Ætérna Christi múnera');
+    expect(invitatoryFullLatin('2026-11-30')).toContain('Regem Apostolórum Dóminum');
+  });
+
+  it('a plain ferial day is unaffected -- still falls through to the plain ferial hymn and invitatory antiphon', () => {
+    expect(hymnLatin(FERIAL_DATE)).toContain('Somno');
+    expect(invitatoryFullLatin(FERIAL_DATE)).toContain('Veníte');
+    expect(invitatoryFullLatin(FERIAL_DATE)).not.toContain('Regem Apostolórum');
+  });
+});