diff --git a/www/settings/post.php b/www/settings/post.php
index fc86b94c..c18f1da2 100644
--- a/www/settings/post.php
+++ b/www/settings/post.php
@@ -1,6 +1,8 @@
 <?
 require_once('Core.php');
 
+use function Safe\strtotime;
+
 $colorScheme = $_POST['color-scheme'] ?? 'auto';
 
 if($colorScheme !== 'dark' && $colorScheme !== 'light' && $colorScheme !== 'auto'){
@@ -9,7 +11,7 @@ if($colorScheme !== 'dark' && $colorScheme !== 'light' && $colorScheme !== 'auto
 
 if($colorScheme == 'auto'){
 	// Delete the cookie; auto is the default
-	setcookie('color-scheme', null, 0, '/', '', true, true);
+	setcookie('color-scheme', '', 0, '/', '', true, true);
 }
 else{
 	setcookie('color-scheme', $colorScheme, strtotime('+10 years'), '/', '', true, true);