diff --git a/src/lib/types.ts b/src/lib/types.ts
index d312b31..57f5f2d 100644
--- a/src/lib/types.ts
+++ b/src/lib/types.ts
@@ -64,7 +64,7 @@ export type WebSocketHook<T = unknown, P = WebSocketEventMap['message'] | null>
   sendMessage: SendMessage,
   sendJsonMessage: SendJsonMessage,
   lastMessage: P,
-  lastJsonMessage: T,
+  lastJsonMessage: T | null,
   readyState: ReadyState,
   getWebSocket: () => (WebSocketLike | null),
 }