diff --git a/guides/subscriptions/subscription_classes.md b/guides/subscriptions/subscription_classes.md
index 45bd054539..8d6d1da0ac 100644
--- a/guides/subscriptions/subscription_classes.md
+++ b/guides/subscriptions/subscription_classes.md
@@ -102,8 +102,8 @@ Like mutations, you can use a generated return type for subscriptions. When you
 
 ```ruby
 class Subscriptions::MessageWasPosted < Subscriptions::BaseSubscription
-  field :room, Types::RoomType, null: true
-  field :message, Types::MessageType, null: true
+  field :room, Types::RoomType, null: false
+  field :message, Types::MessageType, null: false
 end
 ```