diff --git a/doc/arm/Bv9ARM-book.xml b/doc/arm/Bv9ARM-book.xml
index 34a493797d..1766c83bc3 100644
--- a/doc/arm/Bv9ARM-book.xml
+++ b/doc/arm/Bv9ARM-book.xml
@@ -10666,7 +10666,7 @@ example.com                 CNAME   rpz-tcp-only.
 	  <para>
 	    With both methods when named gets a NXDOMAIN response
 	    it examines a seperate namespace to see if the NXDOMAIN
-	    response should be replaced with a alternative response.
+	    response should be replaced with an alternative response.
 	  </para>
 	  <para>
 	    With a redirect zone (<command>zone "." { type redirect; };</command>), the