diff --git a/keyserver/flow-typed/npm/express_v4.17.x.js b/keyserver/flow-typed/npm/express_v4.17.x.js
--- a/keyserver/flow-typed/npm/express_v4.17.x.js
+++ b/keyserver/flow-typed/npm/express_v4.17.x.js
@@ -357,7 +357,10 @@
 
   declare module.exports: {
     // If you try to call like a function, it will use this signature
-    <Req: express$Request, Res: express$Response>(): express$Application<Req, Res>,
+    <
+      Req: express$Request = express$Request,
+      Res: express$Response = express$Response,
+    >(): express$Application<Req, Res>,
     json: (opts: ?JsonOptions) => express$Middleware<>,
     // `static` property on the function
     static: <Req: express$Request, Res: express$Response>(root: string, options?: Object) => express$Middleware<Req, Res>,
diff --git a/services/electron-update-server/flow-typed/npm/express_v4.17.x.js b/services/electron-update-server/flow-typed/npm/express_v4.17.x.js
--- a/services/electron-update-server/flow-typed/npm/express_v4.17.x.js
+++ b/services/electron-update-server/flow-typed/npm/express_v4.17.x.js
@@ -357,7 +357,10 @@
 
   declare module.exports: {
     // If you try to call like a function, it will use this signature
-    <Req: express$Request, Res: express$Response>(): express$Application<Req, Res>,
+    <
+      Req: express$Request = express$Request,
+      Res: express$Response = express$Response,
+    >(): express$Application<Req, Res>,
     json: (opts: ?JsonOptions) => express$Middleware<>,
     // `static` property on the function
     static: <Req: express$Request, Res: express$Response>(root: string, options?: Object) => express$Middleware<Req, Res>,
diff --git a/services/electron-update-server/flow-typed/npm/hazel-server_vx.x.x.js b/services/electron-update-server/flow-typed/npm/hazel-server_vx.x.x.js
--- a/services/electron-update-server/flow-typed/npm/hazel-server_vx.x.x.js
+++ b/services/electron-update-server/flow-typed/npm/hazel-server_vx.x.x.js
@@ -4,6 +4,8 @@
 // flow-typed version: <<STUB>>/hazel-server_v5.1.1/flow_v0.198.1
 
 declare module 'hazel-server' {
+  import type { $Response, $Request } from 'express';
+
   declare export default function hazel(options: {
     interval?: number,
     repository?: string,
@@ -11,5 +13,5 @@
     pre?: boolean,
     token?: string,
     url?: string,
-  }): (Request, Response) => void;
+  }): ($Request, $Response) => void;
 }
diff --git a/services/electron-update-server/index.js b/services/electron-update-server/index.js
--- a/services/electron-update-server/index.js
+++ b/services/electron-update-server/index.js
@@ -1,6 +1,7 @@
 // @flow
 
 import express from 'express';
+import type { $Request, $Response } from 'express';
 import hazel from 'hazel-server';
 
 const hazelServer = hazel({
@@ -11,7 +12,7 @@
 });
 
 const app = express();
-app.all('*', (req, res) => {
+app.all('*', (req: $Request, res: $Response) => {
   hazelServer(req, res);
 });