diff --git a/types/actioncable/index.d.ts b/types/actioncable/index.d.ts
index a48c379c26..d0e2216e73 100644
--- a/types/actioncable/index.d.ts
+++ b/types/actioncable/index.d.ts
@@ -13,7 +13,7 @@ declare module ActionCable {
   }
 
   interface Subscriptions {
-    create(channel: string|ChannelNameWithParams, obj: CreateMixin): Channel;
+    create(channel: string|ChannelNameWithParams, obj?: CreateMixin): Channel;
   }
 
   interface Cable {