diff --git a/guides/source/association_basics.md b/guides/source/association_basics.md
index 860a1e1cba..6fbd52edbd 100644
--- a/guides/source/association_basics.md
+++ b/guides/source/association_basics.md
@@ -505,7 +505,7 @@ class Employee < ApplicationRecord
   has_many :subordinates, class_name: "Employee",
                           foreign_key: "manager_id"
 
-  belongs_to :manager, class_name: "Employee"
+  belongs_to :manager, class_name: "Employee", optional: true
 end
 ```