diff --git a/ch11_blockchain.adoc b/ch11_blockchain.adoc
index cb18fb1a..7d792e06 100644
--- a/ch11_blockchain.adoc
+++ b/ch11_blockchain.adoc
@@ -116,7 +116,7 @@ header. <<block_structure1>> describes how Bitcoin Core stores the structure of
 [[block_header]]
 === Block Header
 
-The block header consists of
+The ((("blocks", "block header")))((("block header")))block header consists of
 block metadata as shown in <<block_header_structure_ch09>>.
 
 ++++