--- a/src/pyams_file/widget/__init__.py	Mon Dec 11 15:26:57 2017 +0100
+++ b/src/pyams_file/widget/__init__.py	Thu Jan 11 17:15:42 2018 +0100
@@ -103,7 +103,7 @@
     def get_thumbnail(self):
         thumbnails = IThumbnail(self.current_value, None)
         if thumbnails is not None:
-            display = thumbnails.get_thumbnail('128x128', 'jpeg')
+            display = thumbnails.get_thumbnail('128x128')
             if display is not None:
                 return '{0}?_={1}'.format(absolute_url(display, self.request), self.timestamp)
         name, ext = os.path.splitext(self.current_value.filename)