diff --git a/lib/library-ext.d.ts b/lib/library-ext.d.ts
index b08d3b242..0d373e22f 100644
--- a/lib/library-ext.d.ts
+++ b/lib/library-ext.d.ts
@@ -4,6 +4,6 @@ import { User } from './models'
 declare module 'express' {
   export interface Request {
     user?: User;
-    flash (type: string, msg: string): any;
+    flash (type: string, msg?: string): any;
   }
 }