diff --git a/upload.php b/upload.php
index 9882d774..7a789dfa 100644
--- a/upload.php
+++ b/upload.php
@@ -47,7 +47,7 @@
                 }
 
                $imageFile = pathinfo($path, PATHINFO_FILENAME);
-               $thumbFile = $dirThumb . $imageFile. '-' . $width . '.jpg';
+               $thumbFile = $dirThumb . $imageFile. '-' . $width . '.webp';
                if (!file_exists($thumbFile)) {
                    create_thumb($path, $width);
                }