diff --git a/ch13_security.adoc b/ch13_security.adoc
index 0f3091ad..9fbe2b0a 100644
--- a/ch13_security.adoc
+++ b/ch13_security.adoc
@@ -190,7 +190,7 @@ we will examine various best practices for practical user security.
 
 ==== Physical Bitcoin Storage
 
-Because most users are far more
+Because most ((("bitcoins", "physical storage")))((("physical bitcoin storage")))users are far more
 comfortable with physical security than information security, a very
 effective method for protecting bitcoins is to convert them into physical
 form. Bitcoin keys, and the seeds used to create them, are nothing more than long numbers. This means that