diff --git a/poky/scripts/lib/wic/ksparser.py b/poky/scripts/lib/wic/ksparser.py
index 05ae292..3453d9c 100644
--- a/poky/scripts/lib/wic/ksparser.py
+++ b/poky/scripts/lib/wic/ksparser.py
@@ -145,7 +145,7 @@
         part.add_argument('--exclude-path', nargs='+')
         part.add_argument('--include-path', nargs='+', action='append')
         part.add_argument('--change-directory')
-        part.add_argument("--extra-space", type=sizetype)
+        part.add_argument("--extra-space", type=sizetype("M"))
         part.add_argument('--fsoptions', dest='fsopts')
         part.add_argument('--fstype', default='vfat',
                           choices=('ext2', 'ext3', 'ext4', 'btrfs',