diff --git a/pages/books/test-driven-development-by-example.mdx b/pages/books/test-driven-development-by-example.mdx
index 9d8717eb..3e70e1c0 100644
--- a/pages/books/test-driven-development-by-example.mdx
+++ b/pages/books/test-driven-development-by-example.mdx
@@ -1002,7 +1002,7 @@
   class Money implements Expression {
     // ...
     reduce(to: string) {
-      const rate = this.currency === "CHF" && to === "USD";
+      const rate = this.currency === "CHF" && to === "USD" ? 2 : 1;
       return new Money(this.amount / rate, to);
     }
   }
@@ -1025,7 +1025,7 @@
   class Money implements Expression {
     // ...
     reduce(bank: Bank, to: string) {
-      const rate = this.currency === "CHF" && to === "USD";
+      const rate = this.currency === "CHF" && to === "USD" ? 2 : 1;
       return new Money(this.amount / rate, to);
     }
   }