diff --git a/ch04.asciidoc b/ch04.asciidoc
index 344740da..b755fe50 100644
--- a/ch04.asciidoc
+++ b/ch04.asciidoc
@@ -383,7 +383,7 @@ Address: 1PRTTaJesdNovgne6Ehcdu1fpEdX7913CK
 
 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. Note that the "raw binary" is not shown in <<table_4-3>> as any encoding for display here would, by definition, not be raw binary data.
 
-We use the((("Bitcoin Explorer","wif-to-ec command")))((("wif-to-ec command (bx)"))) +wif-to-ec+ command from Bitcoin Explorer (see <<libbitcoin>>) to show that both WIF keys represent the same private key:
+We use the((("Bitcoin Explorer","wif-to-ec command")))((("wif-to-ec command (bx)"))) +wif-to-ec+ command from Bitcoin Explorer (see <<appdx_bx>>) to show that both WIF keys represent the same private key:
 
 ----
 $ bx wif-to-ec 5J3mBbAH58CpQ3Y5RNJpUKPE62SQ5tfcvU2JpbnkeyhfsYB1Jcn