diff --git a/bin/tests/system/redirect/conf/bad1.conf b/bin/tests/system/redirect/conf/bad1.conf
index a5f730baa3..141b5f6c5f 100644
--- a/bin/tests/system/redirect/conf/bad1.conf
+++ b/bin/tests/system/redirect/conf/bad1.conf
@@ -25,5 +25,6 @@ zone "." {
 	type redirect;
 	file "redirect.db";
 	allow-query { 10.0.1.0; };
+/* option 'forwarders' is not allowed in 'redirect' zone '.' */
 	forwarders { 1.2.3.4; };
 };
diff --git a/bin/tests/system/redirect/conf/bad2.conf b/bin/tests/system/redirect/conf/bad2.conf
index 2f9c6888d3..e83694bf1e 100644
--- a/bin/tests/system/redirect/conf/bad2.conf
+++ b/bin/tests/system/redirect/conf/bad2.conf
@@ -25,5 +25,6 @@ zone "." {
 	type redirect;
 	file "redirect.db";
 	allow-query { 10.0.1.0; };
+/* option 'also-notify' is not allowed in 'redirect' zone '.' */
 	also-notify { 1.2.3.4; };
 };
diff --git a/bin/tests/system/redirect/conf/bad3.conf b/bin/tests/system/redirect/conf/bad3.conf
index b37ebe91df..fa8746a5b4 100644
--- a/bin/tests/system/redirect/conf/bad3.conf
+++ b/bin/tests/system/redirect/conf/bad3.conf
@@ -21,6 +21,7 @@ zone "." {
 	file "hint.db";
 };
 
+/* redirect zones must be called "." */
 zone "x" {
 	type redirect;
 	file "redirect.db";