diff --git a/book/source/09-verification.md b/book/source/09-verification.md
index 6846a96..33edf6a 100644
--- a/book/source/09-verification.md
+++ b/book/source/09-verification.md
@@ -32,6 +32,7 @@ This is especially the case with signatures created by dedicated signing subkeys
 * **Revocation**:
   Lastly, signatures can be invalidated by revocations.
 
+(temporal-validity)=
 ### Temporal validity
 
 A signature is valid only for a constrained period of time: