diff --git a/book/source/a-artifacts.md b/book/source/a-artifacts.md
index 18df134..914a1d4 100644
--- a/book/source/a-artifacts.md
+++ b/book/source/a-artifacts.md
@@ -41,6 +41,7 @@ FcsHp6K860qG87pDlk2saQIwzXPmQcQvLokbeQMB
 -----END PGP PRIVATE KEY BLOCK-----
 ```
 
+(bob_priv)=
 ## Bob's OpenPGP key
 
 Bob uses passphrase-protected secret key packets. His passphrase is `password`: