diff --git a/ch12_mining.adoc b/ch12_mining.adoc
index 25eea11c..925cf40f 100644
--- a/ch12_mining.adoc
+++ b/ch12_mining.adoc
@@ -73,7 +73,7 @@ exponentially until approximately the year 2140, when all bitcoins
 will have been issued. After 2140, no new bitcoin
 will be issued.
 
-Bitcoin miners also earn fees from transactions. Every transaction may
+Bitcoin miners ((("transaction fees")))also earn fees from transactions. Every transaction may
 include a transaction fee, in the form of a surplus of bitcoins between
 the transaction's inputs and outputs. The winning bitcoin miner gets to
 "keep the change" on the transactions included in the winning block.