diff --git a/preface.asciidoc b/preface.asciidoc
index 58c25ed5..6edad2a3 100644
--- a/preface.asciidoc
+++ b/preface.asciidoc
@@ -11,7 +11,7 @@ Two years later, after creating a number of small startups to explore various bi
 
 This book is mostly intended for coders. If you can use a programming language, this book will teach you how cryptographic currencies work, how to use them, and how to develop software that works with them. The first few chapters are also suitable as an in-depth introduction to bitcoin for noncoders—those trying to understand the inner workings of bitcoin and cryptocurrencies.
 
-===About Early Release books from O'Reilly
+=== About Early Release books from O'Reilly
 
 This is an early release copy of __Mastering Bitcoin__'s second edition. The text, figures, and examples are a work in progress, and several chapters are yet to be revised for this editionn. We are releasing the book before it is finished because we hope that it is already useful in its current form and because we would love your feedback in order to create the best possible finished product.