diff --git a/ch05_wallets.adoc b/ch05_wallets.adoc
index 1bc310d4..f7b5e949 100644
--- a/ch05_wallets.adoc
+++ b/ch05_wallets.adoc
@@ -1366,7 +1366,7 @@ prevent compromise of the master keys.
 
 ===== Index numbers for normal and hardened derivation
 
-The index number used in the derivation function is a 32-bit integer. To
+The index number ((("index numbers", "for hardened derivation", secondary-sortas="hardened derivation")))used in the derivation function is a 32-bit integer. To
 easily distinguish between keys created through the normal derivation
 function versus keys derived through hardened derivation, this index
 number is split into two ranges. Index numbers between 0 and