diff --git a/osm-caching-proxy.php b/osm-caching-proxy.php
index 40ac01c..24c2db0 100644
--- a/osm-caching-proxy.php
+++ b/osm-caching-proxy.php
@@ -16,7 +16,7 @@
 $x = $_GET['x'] ?? '';
 $y = $_GET['y'] ?? '';
 // If any of the variables are empty or not numeric, terminate the script
-if(empty($z) || empty($x) || empty($y) || !is_numeric($z) || !is_numeric($x) || !is_numeric($y) || $z < 0 || $x < 0 || $y < 0) {
+if(!isset($z) || !isset($x) || !isset($y) || !is_numeric($z) || !is_numeric($x) || !is_numeric($y) || $z < 0 || $x < 0 || $y < 0) {
     die;
 }