diff --git a/ch04_keys.adoc b/ch04_keys.adoc
index a2efa80c..04087cc6 100644
--- a/ch04_keys.adoc
+++ b/ch04_keys.adoc
@@ -1423,7 +1423,7 @@ support for new Bitcoin features as soon as they become ((("public key cryptogra
 [[priv_formats]]
 ==== Private Key Formats
 
-The private key
+The ((("private keys", "formats", id="private-key-format")))((("public key cryptography", "private keys", "formats", id="pub-key-private-format")))private key
 can be represented in a number of different formats, all of which
 correspond to the same 256-bit number. <<table_4-2>> shows several common
 formats used to represent private keys. Different formats are used in
@@ -1517,7 +1517,7 @@ See <<hd_wallets>> for more information.
 
 All of these representations are different ways of showing the same
 number, the same private key. They look different, but any one format
-can easily be converted to any other format.
+can easily be converted to any other((("private keys", "formats", startref="private-key-format")))((("public key cryptography", "private keys", "formats", startref="pub-key-private-format"))) format.
 
 [[comp_priv]]
 ==== Compressed Private Keys