diff --git a/book/source/certificates.md b/book/source/certificates.md
index ec7b374..83bac6a 100644
--- a/book/source/certificates.md
+++ b/book/source/certificates.md
@@ -122,7 +122,7 @@ In the {term}`RFC`, the {term}`OpenPGP primary key` is occasionally referred to
 
 Modern {term}`OpenPGP certificates<OpenPGP Certificate>` typically include several {term}`subkeys<OpenPGP Subkey>` in addition to the {term}`primary key<OpenPGP Primary Key>`, although these {term}`subkeys<OpenPGP Subkey>` are optional.
 
-While {term}`subkeys<OpenPGP Subkey>` have the same structural attributes as the {term}`primary key<OpenPGP Primary Key>`, they fulfill  different roles. {term}`Subkeys<OpenPGP Subkey>` are cryptographically linked with the {term}`primary key<OpenPGP Primary Key>`, a relationship further discussed in {numref}`binding-subkeys`.
+While {term}`subkeys<OpenPGP Subkey>` have the same structural attributes as the {term}`primary key<OpenPGP Primary Key>`, they fulfill  different roles. {term}`Subkeys<OpenPGP Subkey>` are cryptographically linked with the {term}`primary key<OpenPGP Primary Key>`, a relationship further discussed in {numref}`bind-subkey`.
 
 ```{figure} plain_svg/Binding_Subkeys.svg
 :name: fig-subkeys