diff --git a/doc/arm/Bv9ARM-book.xml b/doc/arm/Bv9ARM-book.xml
index 1feaa130b5..170cb6d430 100644
--- a/doc/arm/Bv9ARM-book.xml
+++ b/doc/arm/Bv9ARM-book.xml
@@ -4871,6 +4871,7 @@ badresp:1,adberr:0,findfail:0,valfail:0]
max-ncache-ttl number;
max-cache-ttl number;
max-zone-ttl number ;
+ servfail-ttl number;
sig-validity-interval number number ;
sig-signing-nodes number ;
sig-signing-signatures number ;