diff --git a/docs/book/09-Polymorphism.md b/docs/book/09-Polymorphism.md
index 0e4eac6..c865cea 100644
--- a/docs/book/09-Polymorphism.md
+++ b/docs/book/09-Polymorphism.md
@@ -490,7 +490,7 @@ public class PrivateOverride {
     }
 }
 
-public Derived extends PrivateOverride {
+class Derived extends PrivateOverride {
     public void f() {
         System.out.println("public f()");
     }