diff --git a/src/app/portfolio/[slug]/building-passport/[propertyId]/page.tsx b/src/app/portfolio/[slug]/building-passport/[propertyId]/page.tsx
index 92c12eed..ed2080be 100644
--- a/src/app/portfolio/[slug]/building-passport/[propertyId]/page.tsx
+++ b/src/app/portfolio/[slug]/building-passport/[propertyId]/page.tsx
@@ -6,8 +6,10 @@ import {
   SparklesIcon,
   BuildingOfficeIcon,
   ShieldCheckIcon,
+  ExclamationTriangleIcon,
 } from "@heroicons/react/24/outline";
 import { CheckCircleIcon, XCircleIcon } from "@heroicons/react/24/solid";
+import Link from "next/link";
 import {
   getPropertyMeta,
   getConditionReport,
@@ -67,6 +69,43 @@ export default async function BuildingPassportHome(props: {
 }) {
   const params = await props.params;
   const propertyMeta = await getPropertyMeta(params.propertyId);
+
+  // A property with no UPRN isn't matched to an Ordnance Survey address yet, so
+  // the whole UPRN-keyed passport (spatial data, installed measures, EPC) has
+  // nothing to show — and getSpatialData(BigInt(null)) would 500. Surface a
+  // clear "not matched" state and link back to the portfolio instead.
+  if (!propertyMeta.uprn) {
+    return (
+      <div className="max-w-3xl mx-auto px-6 py-16">
+        <div className="rounded-2xl border border-amber-200 bg-amber-50 p-8 text-center shadow-sm">
+          <ExclamationTriangleIcon className="mx-auto h-10 w-10 text-amber-500" />
+          <h1 className="mt-4 text-lg font-bold text-amber-900">
+            Not matched to a UPRN yet
+          </h1>
+          <p className="mx-auto mt-1 max-w-md text-sm text-amber-700">
+            {propertyMeta.address ? (
+              <>
+                <span className="font-medium">{propertyMeta.address}</span>{" "}
+                hasn&apos;t{" "}
+              </>
+            ) : (
+              "This property hasn't "
+            )}
+            been matched to an Ordnance Survey address, so its building passport
+            isn&apos;t available yet. Match it to a UPRN from the portfolio to
+            unlock the passport.
+          </p>
+          <Link
+            href={`/portfolio/${params.slug}`}
+            className="mt-6 inline-flex items-center gap-1.5 rounded-lg bg-amber-600 px-4 py-2 text-sm font-semibold text-white transition-opacity hover:opacity-90"
+          >
+            Back to portfolio
+          </Link>
+        </div>
+      </div>
+    );
+  }
+
   const conditionReport = await getConditionReport(params.propertyId);
   const spatial = await getSpatialData(propertyMeta.uprn);
   const installedMeasures = await getInstalledMeasuresByUprn(Number(propertyMeta.uprn));