diff --git a/book/source/15-migration.md b/book/source/15-migration.md
index 655c07a..6a04389 100644
--- a/book/source/15-migration.md
+++ b/book/source/15-migration.md
@@ -23,6 +23,7 @@ Some of these features require use of new key material, while others can be adop
 A perfect example for a newly introduced feature that can be applied to existing v4 keys are the new SEIPDv2 packets.
 Existing v4 keys can simply announce support for SEIPDv2 via a *Feature* subpacket in a self-signature. This signals to producers, that the users OpenPGP subsystem(s) are capable of handling SEIPDv2.
 
+(migration_s2k)=
 ### Argon2 S2K
 
 Another good example is the Argon2 S2K mechanism.