diff --git a/inc/image.php b/inc/image.php
index c9c35736..a3697e70 100644
--- a/inc/image.php
+++ b/inc/image.php
@@ -311,7 +311,7 @@ class ImageConvert extends ImageBase {
 			$this->destroy();
 		}
 		
-		$this->temp = tempnam($config['tmp'], 'convert');
+		$this->temp = tempnam($config['tmp'], 'convert') . ($config['thumb_ext'] == '' ? '' : '.' . $config['thumb_ext']);
 				
 		$config['thumb_keep_animation_frames'] = (int)$config['thumb_keep_animation_frames'];