diff --git a/nonebot/permission.py b/nonebot/permission.py
index 68c34f82..ac99504b 100644
--- a/nonebot/permission.py
+++ b/nonebot/permission.py
@@ -141,8 +141,8 @@ def USER(*user: str, perm: Optional[Permission] = None):
     """
 
     async def _user(bot: "Bot", event: "Event") -> bool:
-        return bool(event.get_session_id() in user and perm and
-                    await perm(bot, event))
+        return bool(event.get_session_id() in user and (perm is None or
+                    await perm(bot, event)))
 
     return Permission(_user)