diff --git a/boards/signals.py b/boards/signals.py
--- a/boards/signals.py
+++ b/boards/signals.py
@@ -127,6 +127,6 @@ def delete_file(instance, **kwargs):
         if instance.mimetype in FILE_TYPES_IMAGE:
             for size in THUMB_SIZES:
                 file_name_parts = instance.file.name.split('.')
-                thumb_file = MEDIA_ROOT + '{}.{}x{}.{}'.format(file_name_parts[0], *size, file_name_parts[1])
+                thumb_file = MEDIA_ROOT + '{}.{}x{}.{}'.format(file_name_parts[0], size[0], size[1], file_name_parts[1])
                 os.remove(thumb_file)