diff --git a/ch06_transactions.adoc b/ch06_transactions.adoc
index 0bc6c0f2..969569e2 100644
--- a/ch06_transactions.adoc
+++ b/ch06_transactions.adoc
@@ -1038,7 +1038,7 @@ Alice's transaction contains one input and one ((("transactions", "witnesses", s
 [[lock_time]]
 === Lock Time
 
-The final field in a serialized transaction is its lock time.  This
+The ((("transactions", "lock time")))((("lock time")))final field in a serialized transaction is its lock time.  This
 field was part of Bitcoin's original serialization format but it was
 initially only enforced by Bitcoin's policy for choosing which
 transactions to mine.  Bitcoin's earliest known soft fork added a rule