diff --git a/src/gatewayOwnership.ts b/src/gatewayOwnership.ts
index 3c12d1409..2cc266e31 100644
--- a/src/gatewayOwnership.ts
+++ b/src/gatewayOwnership.ts
@@ -96,7 +96,7 @@ export async function acquireGatewayOwnership(input: {
       const alive = existing.hostname !== os.hostname() || isProcessAlive(existing.pid);
       if (alive) {
         throw new Error(
-          `Gateway ownership already held by ${existing.ownerId} on ${existing.hostname} (pid ${existing.pid}). Stop that instance or wait for lease expiry.`
+          `Gateway ownership already held by another instance (id: ${existing.ownerId}). Stop that instance or wait for lease expiry.`
         );
       }
     }
diff --git a/tests/test_gateway_ownership_disclosure.test.ts b/tests/test_gateway_ownership_disclosure.test.ts
new file mode 100644
index 000000000..e9df52d7d
--- /dev/null
+++ b/tests/test_gateway_ownership_disclosure.test.ts
@@ -0,0 +1,29 @@
+import { describe, it, expect } from 'vitest';
+
+function buildOwnershipError(ownerId: string, hostname: string, pid: number): string {
+	return `Gateway ownership already held by another instance (id: ${ownerId}). Stop that instance or wait for lease expiry.`;
+}
+
+describe('gatewayOwnership error message', () => {
+	it('does not include hostname in error', () => {
+		const msg = buildOwnershipError('host123:12345', 'host123', 12345);
+		expect(msg).not.toContain('host123');
+	});
+	it('does not include PID in error', () => {
+		const msg = buildOwnershipError('myhost:9999', 'myhost', 9999);
+		expect(msg).not.toMatch(/\bpid\b/i);
+		expect(msg).not.toContain('9999');
+	});
+	it('includes ownerId opaquely', () => {
+		const msg = buildOwnershipError('abc:1234', 'abc', 1234);
+		expect(msg).toContain('abc:1234');
+	});
+	it('includes lease expiry guidance', () => {
+		const msg = buildOwnershipError('x:1', 'x', 1);
+		expect(msg).toContain('lease expiry');
+	});
+	it('error message is a plain string', () => {
+		const msg = buildOwnershipError('a:1', 'a', 1);
+		expect(typeof msg).toBe('string');
+	});
+});