diff --git a/types/csurf/index.d.ts b/types/csurf/index.d.ts
index 2a626d227b..ee0d18568b 100644
--- a/types/csurf/index.d.ts
+++ b/types/csurf/index.d.ts
@@ -24,7 +24,7 @@ declare module "csurf" {
 
   namespace csurf {
     export interface CookieOptions extends express.CookieOptions {
-      key: string;
+      key?: string;
     }
   }