diff --git a/infra/docker-compose.yml b/infra/docker-compose.yml
index 2529274..ce76cdf 100644
--- a/infra/docker-compose.yml
+++ b/infra/docker-compose.yml
@@ -306,6 +306,9 @@ services:
       Acl__Defaults__Vertrouwelijkheidaanduiding: openbaar
       # Override with the real zaaktype URL after running seed_catalogus.py.
       Acl__Defaults__ZaaktypeUrl: ${ACL_ZAAKTYPE_URL:-http://openzaak:8000/catalogi/api/v1/zaaktypen/00000000-0000-0000-0000-000000000000}
+      # The informatieobjecttype a diploma is filed under (S-10b). Placeholder until seed_catalogus.py
+      # (OZ_PUBLISH=1) reports the real URL, which verify-domain injects like the zaaktype URL.
+      Acl__Defaults__InformatieobjecttypeUrl: ${ACL_INFORMATIEOBJECTTYPE_URL:-http://openzaak:8000/catalogi/api/v1/informatieobjecttypen/00000000-0000-0000-0000-000000000000}
     ports:
       - "8100:8080"
     healthcheck:
diff --git a/infra/openzaak/seed_catalogus.py b/infra/openzaak/seed_catalogus.py
index 5dc15a8..ed4ad67 100644
--- a/infra/openzaak/seed_catalogus.py
+++ b/infra/openzaak/seed_catalogus.py
@@ -124,6 +124,58 @@ def publish_zaaktype(zt):
         print("skip   publish (already published)")
 
 
+def seed_informatieobjecttype(cat, zt):
+    """Create the "Diploma" informatieobjecttype and relate it to the zaaktype (both idempotent).
+
+    A diploma uploaded in S-10b is filed under this informatieobjecttype; OpenZaak only accepts a
+    document (and its zaak relation) once the informatieobjecttype is published AND allowed for the
+    zaak's zaaktype (a zaaktype-informatieobjecttype relation). Both the relation and this call must run
+    while the zaaktype is still a concept, so seed this *before* publishing the zaaktype. Returns the
+    informatieobjecttype dict.
+    """
+    iots = [i for i in find(f"/informatieobjecttypen?catalogus={cat['url']}&status=alles")
+            if i.get("omschrijving") == "Diploma"]
+    if iots:
+        iot = iots[0]
+        print(f"skip   informatieobjecttype Diploma ({iot['url']}) concept={iot.get('concept')}")
+    else:
+        st, iot = api("POST", "/informatieobjecttypen", {
+            "catalogus": cat["url"],
+            "omschrijving": "Diploma",
+            "vertrouwelijkheidaanduiding": "openbaar",
+            "informatieobjectcategorie": "diploma",
+            "beginGeldigheid": "2026-01-01",
+        })
+        if st != 201:
+            sys.exit(f"create informatieobjecttype -> {st}: {json.dumps(iot, indent=2)}")
+        print(f"create informatieobjecttype Diploma ({iot['url']})")
+
+    # Relate it to the zaaktype (must be done while both are concept).
+    relations = find(f"/zaaktype-informatieobjecttypen?zaaktype={zt['url']}&status=alles")
+    if any(r.get("informatieobjecttype") == iot["url"] for r in relations):
+        print("skip   zaaktype-informatieobjecttype Diploma")
+    else:
+        st, body = api("POST", "/zaaktype-informatieobjecttypen", {
+            "zaaktype": zt["url"], "informatieobjecttype": iot["url"],
+            "volgnummer": 1, "richting": "inkomend"})
+        if st != 201:
+            sys.exit(f"relate zaaktype-informatieobjecttype -> {st}: {json.dumps(body, indent=2)}")
+        print("create zaaktype-informatieobjecttype Diploma")
+
+    return iot
+
+
+def publish_informatieobjecttype(iot):
+    """Publish the informatieobjecttype (idempotent) so documents may reference it."""
+    if iot.get("concept", True):
+        st, body = api("POST", f"{iot['url']}/publish")
+        if st != 200:
+            sys.exit(f"publish informatieobjecttype -> {st}: {json.dumps(body, indent=2)}")
+        print(f"publish informatieobjecttype Diploma ({iot['url']})")
+    else:
+        print("skip   publish informatieobjecttype (already published)")
+
+
 def main():
     # 1. Catalogus
     existing = [c for c in find(f"/catalogussen?domein=BIG") if c.get("domein") == "BIG"]
@@ -198,10 +250,16 @@ def main():
     # schema-mandatory" zaaktype S-01 asks for (ADR-0002). Set OZ_PUBLISH=1 to add
     # those relations and publish — needed so a real zaak POST is accepted, which
     # the ACL integration test (S-04a, #46) exercises. See ADR-0006.
+    iot = None
     if PUBLISH:
         # Re-fetch: the bsn-eigenschap branch above may hold a stale concept flag.
         zt = next(z for z in find(f"/zaaktypen?catalogus={cat['url']}&status=alles")
                   if z.get("identificatie") == "BIG-REGISTRATIE")
+        # Seed + relate the Diploma informatieobjecttype (S-10b) while the zaaktype is still concept,
+        # then publish both. Publish the informatieobjecttype before the zaaktype so the zaaktype's
+        # relations reference a published type.
+        iot = seed_informatieobjecttype(cat, zt)
+        publish_informatieobjecttype(iot)
         publish_zaaktype(zt)
 
     # 5. Verify the JWT client can list the zaaktype (concepts included).
@@ -214,6 +272,10 @@ def main():
     # zaaktype URL to configure the ACL's default-fill (ADR-0003/0009).
     zt_url = next(z["url"] for z in zaaktypen if z.get("identificatie") == "BIG-REGISTRATIE")
     print(f"ZAAKTYPE_URL {zt_url}")
+    # Machine-readable informatieobjecttype URL (S-10b) so callers can configure the ACL's document
+    # default-fill. Only emitted when publishing — a concept informatieobjecttype can't back a document.
+    if iot is not None:
+        print(f"INFORMATIEOBJECTTYPE_URL {iot['url']}")
     print(f"OK — BIG catalogus seeded (BIG-REGISTRATIE {state} + bsn eigenschap)")
 
 
diff --git a/infra/run-domain-check.sh b/infra/run-domain-check.sh
index 7294c54..359f65c 100755
--- a/infra/run-domain-check.sh
+++ b/infra/run-domain-check.sh
@@ -33,13 +33,18 @@ echo ">> openzaak=$oz_ip domain=$dom_ip network=$net"
 echo ">> seeding a published BIG zaaktype (idempotent) and capturing its URL"
 sid="$(docker create --network "$net" -e "OZ_BASE=$oz_base" -e OZ_PUBLISH=1 python:3-slim python /seed.py)"
 docker cp "$here/openzaak/seed_catalogus.py" "$sid:/seed.py" >/dev/null
-zt_url="$(docker start -a "$sid" | sed -n 's/^ZAAKTYPE_URL //p' | head -1)"
+seed_out="$(docker start -a "$sid")"
+zt_url="$(printf '%s\n' "$seed_out" | sed -n 's/^ZAAKTYPE_URL //p' | head -1)"
+iot_url="$(printf '%s\n' "$seed_out" | sed -n 's/^INFORMATIEOBJECTTYPE_URL //p' | head -1)"
 docker rm -f "$sid" >/dev/null
 [ -n "$zt_url" ] || { echo "ERROR: seed did not report a ZAAKTYPE_URL" >&2; exit 1; }
+[ -n "$iot_url" ] || { echo "ERROR: seed did not report an INFORMATIEOBJECTTYPE_URL" >&2; exit 1; }
 echo ">> zaaktype: $zt_url"
+echo ">> informatieobjecttype: $iot_url"
 
-echo ">> recreating the acl service pointed at the seeded zaaktype (host-consistent)"
-ACL_ZAAKTYPE_URL="$zt_url" ACL_OPENZAAK_BASEURL="$oz_base/" docker compose -f "$compose" up -d acl
+echo ">> recreating the acl service pointed at the seeded zaaktype + informatieobjecttype (host-consistent)"
+ACL_ZAAKTYPE_URL="$zt_url" ACL_INFORMATIEOBJECTTYPE_URL="$iot_url" ACL_OPENZAAK_BASEURL="$oz_base/" \
+  docker compose -f "$compose" up -d acl
 WAIT_TIMEOUT="${WAIT_TIMEOUT:-120}" bash "$here/wait-healthy.sh" acl
 
 echo ">> submitting a registration to the domain"