diff --git a/apps/dashboard/src/routes/(org-site)/+layout.server.ts b/apps/dashboard/src/routes/(org-site)/+layout.server.ts
new file mode 100644
index 00000000..d1079dcf
--- /dev/null
+++ b/apps/dashboard/src/routes/(org-site)/+layout.server.ts
@@ -0,0 +1,13 @@
+import { error } from '@sveltejs/kit';
+
+export const load = async ({ parent }) => {
+  const { org, isOrgSite } = await parent();
+
+  // An org-site subdomain that doesn't resolve to a real org must 404 rather
+  // than fall back to whatever org a requested course happens to belong to.
+  if (isOrgSite && !org) {
+    throw error(404, 'Organization not found');
+  }
+
+  return {};
+};