diff --git a/src/main/asciidoc/index.adoc b/src/main/asciidoc/index.adoc
index edb4542..47b2958 100644
--- a/src/main/asciidoc/index.adoc
+++ b/src/main/asciidoc/index.adoc
@@ -3,6 +3,7 @@
 Rob Winch, Vedran Pavić, Jakub Kubrynski, Greg Turnquist
 :doctype: book
 :toc: left
+:toclevels: 4
 
 [[abstract]]
 
@@ -59,7 +60,7 @@ If you would like to provide custom Jackson modules you can do it by explicitly
 include::{code-dir}/src/test/java/org/springframework/session/data/mongo/integration/MongoRepositoryJacksonITest.java[tag=sample]
 ----
 
-==== JdkMongoSessionConverter
+===== JdkMongoSessionConverter
 
 `JdkMongoSessionConverter` uses standard Java serialization to persist session attributes map to MongoDB in a binary form.
 However, standard session elements like id, access time, etc are still written as a plain Mongo objects and can be read and queried without additional effort.