diff --git a/book/source/adv/certificates.md b/book/source/adv/certificates.md
index 3bfadf5..dfa982d 100644
--- a/book/source/adv/certificates.md
+++ b/book/source/adv/certificates.md
@@ -170,7 +170,7 @@ This variance underscores the importance of understanding your specific GnuPG co
 
 [^gpg-default-strip]: GnuPG's changes in the default handling of third-party certifications on imports were prompted by the 2019 [keyserver flooding event](https://dev.gnupg.org/T4607#127792).
 
-### Minimization for email: Use cases and considerations
+## Minimization for email: Use cases and considerations
 
 Certificate minimization plays a critical role in email communications. By reducing certificate size, email clients can improve performance and enhance security. However, certificate minimization strategies may vary, depending on the use case and with consideration given to the balance between usability and security.