diff --git a/src/Point.php b/src/Point.php
index 6353da4..a94653e 100644
--- a/src/Point.php
+++ b/src/Point.php
@@ -19,7 +19,7 @@ class Point extends Data
         ]);
     }
 
-    public function markerUrl(string $zoom = 20): string
+    public function markerUrl(string $zoom = '20'): string
     {
         return '/osm-static-maps/?' . http_build_query([
             'geojson' => json_encode(['type' => 'Point', 'coordinates' => [$this->lon, $this->lat]]),