diff --git a/inc/instance-config.php b/inc/instance-config.php
index 46438b2f..1f8d2811 100644
--- a/inc/instance-config.php
+++ b/inc/instance-config.php
@@ -168,7 +168,7 @@ $config['max_images'] = 5;
 $config['image_reject_repost'] = false;
 
 $config['thumb_method'] = 'gm+gifsicle';
-$config['thumb_ext'] = 'webp';
+$config['thumb_ext'] = 'png';
 $config['gnu_md5'] = '1';