diff --git a/TODO.md b/TODO.md
index b102042..52d22c5 100644
--- a/TODO.md
+++ b/TODO.md
@@ -213,11 +213,28 @@ Urban I/Eleutherius/John I do have content -- they just needed a very
 late test year). Every pre-existing antiphon file that predated this
 pass has now been checked against a live Monastic query; most needed
 correction (confirmed Roman-rite sourced), a handful already matched.
-- **All ~52 temporal entries: done** (see the section above for method and
-  the one deliberate exception, `christmas-octave-sunday`).
+- **All ~52 temporal entries: done, including `christmas-octave-sunday`**
+  (see the section above for method and its own correction).
 - **94 `propers: null` saints: not started** — need a collect authored (a
   bigger, separate task) before an antiphon id even has anywhere to attach.
 
+### Bug found and fixed while pulling christmas-octave-sunday's antiphon
+
+`data/calendar/temporal-categories.yml` had christmastide's own Sunday
+coded `privileged-sunday` (Advent's tier — never displaced short of
+Duplex-majus+, and even then only commemorated in return). Live-checking
+all three Duplex-II-classis "Comites Christi" collision dates (St.
+Stephen/John/Holy Innocents falling on the Sunday, plus St. Silvester,
+plain Duplex) showed the exact reverse: the saint wins outright every
+time, the Sunday only commemorated — `ordinary-sunday`'s rule, not
+`privileged-sunday`'s. Fixed by reclassifying christmastide's `sunday` to
+`ordinary-sunday` (the `feria` side, `privileged-feria-minor`, was
+already correct and untouched). New tests in
+`tests/calendar/december-sanctoral.test.ts` cover both directions: the
+saint winning on the three verified collision dates, and St. Thomas
+Becket (Semiduplex) still transferring off the Sunday rather than
+winning, unchanged by the fix.
+
 ### Bug found while checking February's results, not yet fixed
 
 `hours/resolve-common.ts`'s `splitNamedAntiphon` always marks its output
diff --git a/src/data/calendar/temporal-categories.yml b/src/data/calendar/temporal-categories.yml
index 295faf0..946a0a7 100644
--- a/src/data/calendar/temporal-categories.yml
+++ b/src/data/calendar/temporal-categories.yml
@@ -52,7 +52,21 @@ bySeason:
   # Canterbury, Semiduplex, wins outright within the Octave (Dec 29) in the
   # real Monastic 1617 engine, which `privileged-feria`'s Duplex+ threshold
   # would wrongly forbid.
-  christmastide: { sunday: privileged-sunday, feria: privileged-feria-minor }
+  #
+  # The Sunday itself is `ordinary-sunday`, NOT `privileged-sunday` —
+  # originally miscoded as privileged-sunday (Advent's own Sundays' tier),
+  # which was backwards: live-verified against all six possible collision
+  # dates (Dec 26 St. Stephen, 27 St. John, 28 Holy Innocents — all
+  # Duplex-II-classis — plus 31 St. Silvester, plain Duplex), every one of
+  # them wins outright over the Sunday, which is merely commemorated in
+  # return — exactly ordinary-sunday's Duplex+ rule, and the reverse of
+  # privileged-sunday's (which would keep the Sunday primary and only nod
+  # to the saint). Dec 29 (St. Thomas Becket, Semiduplex) still transfers
+  # off the Sunday rather than winning, and a day with no saint at all
+  # (e.g. Dec 30) still resolves to the Sunday cleanly — both of those
+  # match ordinary-sunday too, so nothing here actually depended on the
+  # stronger tier.
+  christmastide: { sunday: ordinary-sunday, feria: privileged-feria-minor }
   epiphanytide: { sunday: ordinary-sunday, feria: ordinary-feria }
   septuagesima: { sunday: privileged-sunday, feria: ordinary-feria }
   lent: { sunday: privileged-sunday, feria: ordinary-feria }
diff --git a/tests/calendar/december-sanctoral.test.ts b/tests/calendar/december-sanctoral.test.ts
index f965b37..756dcd1 100644
--- a/tests/calendar/december-sanctoral.test.ts
+++ b/tests/calendar/december-sanctoral.test.ts
@@ -108,6 +108,62 @@ describe('December sanctoral pull (first pass, 12/12)', () => {
     ]);
   });
 
+  it('the Christmas Octave Sunday loses outright to a Duplex+ Comites Christi feast when the two collide -- ordinary-sunday, not privileged-sunday', () => {
+    // Corrects a real bug: christmastide's Sunday was originally coded
+    // privileged-sunday (Advent's own tier), which would have kept the
+    // Sunday primary here with the saint merely commemorated -- backwards
+    // from the live Monastic 1617 engine, which was checked directly
+    // against all three Duplex-II-classis collision dates and shows the
+    // saint winning outright every time, the Sunday only commemorated.
+    const stephenSunday = resolveDay('2021-12-26');
+    expect(stephenSunday.winner).toEqual({
+      kind: 'sanctoral',
+      id: 'st-stephen-protomartyr',
+      name: 'St. Stephen, Protomartyr',
+      rank: 'duplex-2-classis',
+    });
+    expect(stephenSunday.commemorations).toContainEqual({ kind: 'temporal', id: 'christmas-octave-sunday' });
+
+    const innocentsSunday = resolveDay('2025-12-28');
+    expect(innocentsSunday.winner).toEqual({
+      kind: 'sanctoral',
+      id: 'holy-innocents',
+      name: 'The Holy Innocents, Martyrs',
+      rank: 'duplex-2-classis',
+    });
+    expect(innocentsSunday.commemorations).toContainEqual({ kind: 'temporal', id: 'christmas-octave-sunday' });
+
+    // A plain Duplex (not just Duplex-II-classis) is still enough: St.
+    // Silvester (Dec 31) wins outright the same way when it falls on the
+    // Sunday, also live-verified.
+    const silvesterSunday = resolveDay('2023-12-31');
+    expect(silvesterSunday.winner).toEqual({
+      kind: 'sanctoral',
+      id: 'st-silvester-i',
+      name: 'St. Silvester I, Pope and Confessor',
+      rank: 'duplex',
+    });
+    expect(silvesterSunday.commemorations).toContainEqual({ kind: 'temporal', id: 'christmas-octave-sunday' });
+  });
+
+  it('the Christmas Octave Sunday still keeps a lesser feast from winning, same as before the ordinary-sunday fix', () => {
+    // St. Thomas Becket (Semiduplex, Dec 29) transfers off the Sunday
+    // rather than winning it -- unaffected by the privileged->ordinary
+    // change, since both tiers transfer a Semiduplex here; this test
+    // guards against a regression the other direction.
+    const beckettSunday = resolveDay('2024-12-29');
+    expect(beckettSunday.winner.kind).toBe('temporal');
+    expect(beckettSunday.commemorations.some((c) => c.kind === 'sanctoral')).toBe(false);
+    // St. Thomas still gets his day -- pushed to the next open one.
+    const transferred = resolveDay('2024-12-30');
+    expect(transferred.winner).toEqual({
+      kind: 'sanctoral',
+      id: 'st-thomas-becket',
+      name: 'St. Thomas of Canterbury, Bishop and Martyr',
+      rank: 'semiduplex',
+    });
+  });
+
   it('the Christmas Octave commemorations build up day by day as each Comites Christi feast starts its own octave', () => {
     // Same clean year (2033) as above, walking the whole week to show the
     // accumulation directly -- this is the concrete shape of "commemorations