diff --git a/src/data/propers/common/opening-domine-labia.yml b/src/data/propers/common/opening-domine-labia.yml
new file mode 100644
index 0000000..1bf00c2
--- /dev/null
+++ b/src/data/propers/common/opening-domine-labia.yml
@@ -0,0 +1,27 @@
+# Verified against Divinum Officium (Monastic Tridentinum 1617), 2026-09-02.
+# Matins-only, unlike opening-alleluia.yml/opening-laus-tibi.yml (shared
+# across every hour). In the Monastic rite this versicle follows "Deus in
+# adjutórium" (rather than preceding it, as in the Roman/secular rite) and
+# is recited three times ("iij" rubric) — see
+# divinum-officium-reference/web/www/horas/Ordinarium/Matutinum.txt.
+# No repeated Gloria Patri is needed here since it was already said with
+# "Deus in adjutórium" immediately before this block.
+id: opening-domine-labia
+text:
+  la: |
+    V. Dómine, lábia mea apéries.
+    R. Et os meum annuntiábit laudem tuam.
+    V. Dómine, lábia mea apéries.
+    R. Et os meum annuntiábit laudem tuam.
+    V. Dómine, lábia mea apéries.
+    R. Et os meum annuntiábit laudem tuam.
+  en: |
+    V. O Lord, open Thou my lips.
+    R. And my mouth shall declare Thy praise.
+    V. O Lord, open Thou my lips.
+    R. And my mouth shall declare Thy praise.
+    V. O Lord, open Thou my lips.
+    R. And my mouth shall declare Thy praise.
+status:
+  la: verified
+  en: verified
diff --git a/src/hours/matins.ts b/src/hours/matins.ts
index e1cfe2c..83005e0 100644
--- a/src/hours/matins.ts
+++ b/src/hours/matins.ts
@@ -756,6 +756,7 @@ export function resolveOrdo(date: string): ResolvedOrdo {
     ? []
     : [
         { kind: 'versicle', text: resolveCommon(getOpeningVersicleId(day.season, day.winner)) },
+        { kind: 'versicle', text: resolveCommon('opening-domine-labia') },
         plainPsalm(3),
         { kind: 'section-heading', label: 'Invitatory' },
         ...invitatoryParts(day),