diff --git a/src/gateway/server-tailscale.test.ts b/src/gateway/server-tailscale.test.ts
index 20bb0790133..33b97f4a057 100644
--- a/src/gateway/server-tailscale.test.ts
+++ b/src/gateway/server-tailscale.test.ts
@@ -5,7 +5,7 @@ const mocks = vi.hoisted(() => ({
   disableTailscaleServe: vi.fn(async () => undefined),
   enableTailscaleFunnel: vi.fn(async (_port: number) => undefined),
   disableTailscaleFunnel: vi.fn(async () => undefined),
-  getTailnetHostname: vi.fn(async () => null),
+  getTailnetHostname: vi.fn<() => Promise<string | null>>(async () => null),
   hasTailscaleFunnelRouteForPort: vi.fn(async (_port: number) => false),
 }));