diff --git a/backend/src/routes/tenant.ts b/backend/src/routes/tenant.ts
index f2c363dc..15a2d295 100644
--- a/backend/src/routes/tenant.ts
+++ b/backend/src/routes/tenant.ts
@@ -278,6 +278,11 @@ export default async function tenantRoutes(server: FastifyInstance) {
 
             if (!data) return reply.code(400).send({ error: "data required" })
 
+            if (data.businessInfo && Object.prototype.hasOwnProperty.call(data.businessInfo, "outgoingEInvoiceEnabled")
+                && typeof data.businessInfo.outgoingEInvoiceEnabled !== "boolean") {
+                return reply.code(400).send({ error: "Die Einstellung für Ausgangs-E-Rechnungen muss ein Wahrheitswert sein." })
+            }
+
             if (Object.prototype.hasOwnProperty.call(data, "portalConfig")) {
                 const config = data.portalConfig
                 if (!config || typeof config !== "object" || Array.isArray(config)