diff --git a/book/source/04-certificates.md b/book/source/04-certificates.md
index df3d27f..c73f079 100644
--- a/book/source/04-certificates.md
+++ b/book/source/04-certificates.md
@@ -201,7 +201,7 @@ It is crucial to note that the components of an OpenPGP certificate remain stati
 :name: fig-primary-metadata
 :alt: Depicts a direct key signature, associated with a primary component key.
 
-Metadata can be associated with the primary key using a *direct key signature*
+Metadata can be associated with the primary key using a *direct key signature*.
 ```
 
 ### Defining operational capabilities of component keys with key flags