diff --git a/ch06_transactions.adoc b/ch06_transactions.adoc
index b657478a..cff66633 100644
--- a/ch06_transactions.adoc
+++ b/ch06_transactions.adoc
@@ -62,7 +62,7 @@ use this format.
 
 [TIP]
 ====
-The only other widely used transaction serialization format of that
+The only ((("partially signed bitcoin transaction (PSBT) format")))((("PSBT (partially signed bitcoin transaction) format")))other widely used transaction serialization format of that
 we're aware of is the partially signed bitcoin transaction (PSBT) format
 documented in BIPs 174 and 370 (with extensions documented in other
 BIPs).  PSBT allows an untrusted program to produce a transaction