diff --git a/fn/ns.php b/fn/ns.php
index 9ee5b8e..30fc277 100644
--- a/fn/ns.php
+++ b/fn/ns.php
@@ -1,30 +1,21 @@
 <?php
 
-define('SOA_VALUES', [
+const SOA_VALUES = [
 	'ttl' => 10800,
 	'email' => CONF['ns']['public_soa_email'],
 	'refresh' => 10800,
 	'retry' => 3600,
 	'expire' => 3628800,
 	'negative' => 10800,
-]);
+];
 
-define('MIN_TTL', 300);
-define('DEFAULT_TTL', 10800);
-define('MAX_TTL', 1728000);
+const MIN_TTL = 300;
+const DEFAULT_TTL = 10800;
+const MAX_TTL = 1728000;
 
-define('ALLOWED_TYPES', ['AAAA', 'A', 'TXT', 'SRV', 'MX', 'SVCB', 'HTTPS', 'NS', 'DS', 'CAA', 'CNAME', 'DNAME', 'LOC', 'SSHFP', 'TLSA']);
+const ALLOWED_TYPES = ['AAAA', 'A', 'TXT', 'SRV', 'MX', 'SVCB', 'HTTPS', 'NS', 'DS', 'CAA', 'CNAME', 'DNAME', 'LOC', 'SSHFP', 'TLSA'];
 
-define('ZONE_MAX_CHARACTERS', 10000);
-
-function nsCommonRequirements() {
-	return (isset($_POST['action'])
-		AND isset($_POST['zone'])
-		AND isset($_POST['ttl-value'])
-		AND isset($_POST['ttl-multiplier'])
-		AND isset($_SESSION['id'])
-	);
-}
+const ZONE_MAX_CHARACTERS = 10000;
 
 function nsParseCommonRequirements() {
 	nsCheckZonePossession($_POST['zone']);
@@ -34,7 +25,7 @@ function nsParseCommonRequirements() {
 	else
 		$values['domain'] = formatAbsoluteDomain(formatEndWithDot($_POST['subdomain']) . $_POST['zone']);
 
-	$values['ttl'] = $_POST['ttl-value'] * $_POST['ttl-multiplier'];
+	$values['ttl'] = intval($_POST['ttl-value'] * $_POST['ttl-multiplier']);
 
 	if ($values['ttl'] < MIN_TTL)
 		output(403, sprintf(_('TTLs shorter than %s seconds are forbidden.'), MIN_TTL));
@@ -58,14 +49,18 @@ function nsCheckZonePossession($zone) {
 }
 
 function nsDeleteZone($zone) {
-	// Delete zone data
-	exec(CONF['dns']['knotc_path'] . ' --blocking --timeout 3 --force zone-purge ' . $zone, result_code: $code);
-	if ($code !== 0)
-		output(500, 'Failed to purge zone data.');
-
 	// Remove from Knot configuration
 	knotcConfExec(["unset 'zone[$zone]'"]);
 
+	// Remove Knot zone file
+	if (unlink(CONF['ns']['knot_zones_path'] . '/' . $zone . 'zone') !== true)
+		output(500, 'Failed to remove Knot zone file.');
+
+	// Remove Knot related data
+	exec(CONF['dns']['knotc_path'] . ' --blocking --timeout 3 --force zone-purge ' . $zone . ' +orphan', result_code: $code);
+	if ($code !== 0)
+		output(500, 'Failed to purge zone data.');
+
 	// Remove from database
 	query('delete', 'zones', [
 		'zone' => $zone,