diff --git a/app/controllers/invoicecontroller.js b/app/controllers/invoicecontroller.js
index 54bed08..d8e60a8 100644
--- a/app/controllers/invoicecontroller.js
+++ b/app/controllers/invoicecontroller.js
@@ -78,8 +78,14 @@ exports.getById = async (req, res) => {
     if (!isMaster) {
         const authCompanyId = await GetCompanyId(authKey);
         const invCompanyId = await GetCompanyIdByCustomerId(invoice.invCustId);
+        // Cross-tenant access is reported as 404, not 403 — otherwise
+        // a scoped caller can enumerate which Invoice ids are
+        // populated across the whole tenant table by status code.
+        // Same secure-404 pattern as the prior 11 entities (#174 /
+        // #188 / #192 / #196 / #200 / #204 / #210 / #214 / #218 /
+        // #222 / #226).
         if (authCompanyId === -1 || invCompanyId === -1 || authCompanyId !== invCompanyId) {
-            return res.status(403).json({ message: "Invalid Authorization Key." });
+            return res.status(404).json({ message: "Not found." });
         }
     }
     return res.status(200).json({ message: "Found.", invoice });
@@ -153,8 +159,9 @@ exports.update = async (req, res) => {
     if (!isMaster) {
         const authCompanyId = await GetCompanyId(authKey);
         const invCompanyId = await GetCompanyIdByCustomerId(invoice.invCustId);
+        // Secure-404 on PATCH for the same reason as GET.
         if (authCompanyId === -1 || invCompanyId === -1 || authCompanyId !== invCompanyId) {
-            return res.status(403).json({ message: "Invalid Authorization Key." });
+            return res.status(404).json({ message: "Not found." });
         }
     }
 
@@ -197,8 +204,9 @@ exports.remove = async (req, res) => {
     if (!isMaster) {
         const authCompanyId = await GetCompanyId(authKey);
         const invCompanyId = await GetCompanyIdByCustomerId(invoice.invCustId);
+        // Secure-404 on DELETE for the same reason as GET / PATCH.
         if (authCompanyId === -1 || invCompanyId === -1 || authCompanyId !== invCompanyId) {
-            return res.status(403).json({ message: "Invalid Authorization Key." });
+            return res.status(404).json({ message: "Not found." });
         }
     }
 
diff --git a/tests/api/invoice.test.js b/tests/api/invoice.test.js
index 6043c00..7ecf331 100644
--- a/tests/api/invoice.test.js
+++ b/tests/api/invoice.test.js
@@ -120,3 +120,93 @@ describe('Invoice body validation', () => {
         expect(issue).toBeDefined();
     });
 });
+
+describe('Invoice tenant-enumeration defense (secure 404)', () => {
+    // Customer-cascade-scoped: invCustId → customer.custCompId.
+    // Spy on getCompanyIdByCustomerId so the cascade resolves to a
+    // different company than the caller's.
+    test('controller getById: existing-but-not-yours returns 404 to non-master', async () => {
+        const auth = require('../../app/middleware/auth.js');
+        const controller = require('../../app/controllers/invoicecontroller.js');
+        const isMasterSpy = vi.spyOn(auth, 'isMaster').mockResolvedValue(false);
+        const getCompanyIdSpy = vi.spyOn(auth, 'getCompanyId').mockResolvedValue(7);
+        const getCompanyIdByCustomerIdSpy = vi.spyOn(auth, 'getCompanyIdByCustomerId').mockResolvedValue(99);
+        try {
+            const db = require('../../app/config/db.config.js');
+            db.Invoice.findByPk = vi.fn().mockResolvedValue({
+                invId: 42, invCustId: 13, invArch: false,
+            });
+            const req = { get: (h) => (h === 'authKey' ? 'scoped-to-7' : undefined), params: { id: 42 } };
+            let captured = null;
+            const res = {
+                status(code) { this._code = code; return this; },
+                json(body) { captured = { code: this._code, body }; return this; },
+            };
+            await controller.getById(req, res);
+            expect(captured.code).toBe(404);
+            expect(captured.body.message).toMatch(/not found/i);
+        } finally {
+            isMasterSpy.mockRestore();
+            getCompanyIdSpy.mockRestore();
+            getCompanyIdByCustomerIdSpy.mockRestore();
+        }
+    });
+
+    test('controller update: existing-but-not-yours returns 404 to non-master', async () => {
+        const auth = require('../../app/middleware/auth.js');
+        const controller = require('../../app/controllers/invoicecontroller.js');
+        const isMasterSpy = vi.spyOn(auth, 'isMaster').mockResolvedValue(false);
+        const getCompanyIdSpy = vi.spyOn(auth, 'getCompanyId').mockResolvedValue(7);
+        const getCompanyIdByCustomerIdSpy = vi.spyOn(auth, 'getCompanyIdByCustomerId').mockResolvedValue(99);
+        try {
+            const db = require('../../app/config/db.config.js');
+            db.Invoice.findByPk = vi.fn().mockResolvedValue({
+                invId: 42, invCustId: 13, invArch: false, update: vi.fn(),
+            });
+            const req = {
+                get: (h) => (h === 'authKey' ? 'scoped-to-7' : undefined),
+                params: { id: 42 },
+                body: { invPaid: true },
+            };
+            let captured = null;
+            const res = {
+                status(code) { this._code = code; return this; },
+                json(body) { captured = { code: this._code, body }; return this; },
+            };
+            await controller.update(req, res);
+            expect(captured.code).toBe(404);
+            expect(captured.body.message).toMatch(/not found/i);
+        } finally {
+            isMasterSpy.mockRestore();
+            getCompanyIdSpy.mockRestore();
+            getCompanyIdByCustomerIdSpy.mockRestore();
+        }
+    });
+
+    test('controller remove: existing-but-not-yours returns 404 to non-master', async () => {
+        const auth = require('../../app/middleware/auth.js');
+        const controller = require('../../app/controllers/invoicecontroller.js');
+        const isMasterSpy = vi.spyOn(auth, 'isMaster').mockResolvedValue(false);
+        const getCompanyIdSpy = vi.spyOn(auth, 'getCompanyId').mockResolvedValue(7);
+        const getCompanyIdByCustomerIdSpy = vi.spyOn(auth, 'getCompanyIdByCustomerId').mockResolvedValue(99);
+        try {
+            const db = require('../../app/config/db.config.js');
+            db.Invoice.findByPk = vi.fn().mockResolvedValue({
+                invId: 42, invCustId: 13, invArch: false, update: vi.fn(),
+            });
+            const req = { get: (h) => (h === 'authKey' ? 'scoped-to-7' : undefined), params: { id: 42 } };
+            let captured = null;
+            const res = {
+                status(code) { this._code = code; return this; },
+                json(body) { captured = { code: this._code, body }; return this; },
+            };
+            await controller.remove(req, res);
+            expect(captured.code).toBe(404);
+            expect(captured.body.message).toMatch(/not found/i);
+        } finally {
+            isMasterSpy.mockRestore();
+            getCompanyIdSpy.mockRestore();
+            getCompanyIdByCustomerIdSpy.mockRestore();
+        }
+    });
+});