diff --git a/docs/examples/hook.sh b/docs/examples/hook.sh
index 52f93094..626ad3a4 100755
--- a/docs/examples/hook.sh
+++ b/docs/examples/hook.sh
@@ -138,6 +138,8 @@ request_failure() {
     #   The specified reason for the error.
     # - REQTYPE
     #   The kind of request that was made (GET, POST...)
+    # - HEADERS
+    #   HTTP headers returned by the CA
 
     # Simple example: Send mail to root
     # printf "Subject: HTTP request failed failed!\n\nA http request failed with status ${STATUSCODE}!" | sendmail root