diff --git a/types.ts b/types.ts
index 4c261cb6..8f108f19 100644
--- a/types.ts
+++ b/types.ts
@@ -46,6 +46,7 @@ export type Key = string | number[] | ArrayBuffer | Uint8ArrayArrayBuffer;
 
 export interface UpgradeWebSocketOptions {
   protocol?: string;
+  idleTimeout?: number;
 }
 
 export type UpgradeWebSocketFn = (