diff --git a/ch04_keys.adoc b/ch04_keys.adoc
index 089f9015..1b158c5e 100644
--- a/ch04_keys.adoc
+++ b/ch04_keys.adoc
@@ -638,7 +638,7 @@ shows the full base58 alphabet.
 ====
 
 To add extra security against typos or transcription errors, base58check
-includes a _checksum_ encoded in the base58 alphabet. The checksum is an
+includes((("checksums"))) a _checksum_ encoded in the base58 alphabet. The checksum is an
 additional four bytes
 added to the end of the data that is being encoded. The checksum is
 derived from the hash of the encoded data and can therefore be used to