diff --git a/app/controllers/companycontroller.js b/app/controllers/companycontroller.js
index 536506c..2c8b10e 100644
--- a/app/controllers/companycontroller.js
+++ b/app/controllers/companycontroller.js
@@ -75,8 +75,15 @@ exports.getById = async (req, res) => {
     const isMaster = await IsMaster(authKey);
     if (!isMaster) {
         const companyId = await GetCompanyId(authKey);
+        // Cross-tenant access (caller's company doesn't match the
+        // looked-up company) is reported as 404, not 403. Returning
+        // 403 here would let a non-master caller enumerate which
+        // companies exist by probing IDs: 403 = "this company exists
+        // but isn't yours", 404 = "doesn't exist at all". Collapse
+        // both into 404 so the API doesn't leak the size of the
+        // tenant table to scoped keys.
         if (companyId === -1 || company.compId !== companyId) {
-            return res.status(403).json({ message: "Invalid Authorization Key." });
+            return res.status(404).json({ message: "Not found." });
         }
     }
     return res.status(200).json({ message: "Found.", company });
@@ -142,8 +149,11 @@ exports.update = async (req, res) => {
     const isMaster = await IsMaster(authKey);
     if (!isMaster) {
         const companyId = await GetCompanyId(authKey);
+        // Same secure-404 pattern as getById: don't let a non-master
+        // caller distinguish "this company exists but isn't yours"
+        // from "this id doesn't exist" by status code.
         if (companyId === -1 || company.compId !== companyId) {
-            return res.status(403).json({ message: "Invalid Authorization Key." });
+            return res.status(404).json({ message: "Not found." });
         }
     }
 
diff --git a/tests/api/company.test.js b/tests/api/company.test.js
index 24a209b..1c80435 100644
--- a/tests/api/company.test.js
+++ b/tests/api/company.test.js
@@ -76,6 +76,84 @@ describe('Company route mounting', () => {
     });
 });
 
+describe('Company tenant-enumeration defense (secure 404)', () => {
+    // Unit-level: exercise the controller's getById/update directly with
+    // a stub `res` and an explicit `Company` model whose findByPk
+    // returns the "exists but not yours" shape. Sidesteps the HTTP
+    // pipeline so we don't have to wire every upstream middleware
+    // through testing seams — the assertion is just about the response
+    // code the controller chose for the cross-tenant branch.
+    //
+    // Why test at this level
+    //   The HTTP-level mock used by the other tests in this file makes
+    //   `Company.findByPk` resolve to `null` by default, which the
+    //   controller short-circuits to a 404 BEFORE the cross-tenant
+    //   branch is reached. Driving findByPk to return a populated row
+    //   from the HTTP layer requires reaching deep into vitest module
+    //   state in a way that fights vi.mock's hoisting; the controller-
+    //   level test below pins the same behavioral guarantee much more
+    //   cleanly.
+
+    test('controller getById: existing-but-not-yours returns 404 to non-master', async () => {
+        // Use the exposed _internals seam (companycontroller.js:198).
+        // The controller's getById path uses IsMaster + GetCompanyId
+        // captured as module-locals; we can't rebind those across the
+        // ESM boundary, so we drive them indirectly by spying on
+        // auth.js's own exports — the helpers the captured locals point
+        // to.
+        const auth = require('../../app/middleware/auth.js');
+        const controller = require('../../app/controllers/companycontroller.js');
+        const isMasterSpy = vi.spyOn(auth, 'isMaster').mockResolvedValue(false);
+        const getCompanyIdSpy = vi.spyOn(auth, 'getCompanyId').mockResolvedValue(7);
+        try {
+            const db = require('../../app/config/db.config.js');
+            db.Company.findByPk = vi.fn().mockResolvedValue({ compId: 99, compArch: false });
+
+            const req = { get: (h) => (h === 'authKey' ? 'scoped-to-7' : undefined), params: { id: 99 } };
+            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();
+        }
+    });
+
+    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/companycontroller.js');
+        const isMasterSpy = vi.spyOn(auth, 'isMaster').mockResolvedValue(false);
+        const getCompanyIdSpy = vi.spyOn(auth, 'getCompanyId').mockResolvedValue(7);
+        try {
+            const db = await import('../../app/config/db.config.js');
+            db.Company.findByPk = vi.fn().mockResolvedValue({
+                compId: 99, compArch: false, update: vi.fn(),
+            });
+            const req = {
+                get: (h) => (h === 'authKey' ? 'scoped-to-7' : undefined),
+                params: { id: 99 },
+                body: { compName: 'X' },
+            };
+            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();
+        }
+    });
+});
+
 describe('Company body validation', () => {
     test('POST rejects unknown field with 400', async () => {
         const res = await request(app)