diff --git a/youtube_dl/FileDownloader.py b/youtube_dl/FileDownloader.py
index 7139adf6b..100779756 100644
--- a/youtube_dl/FileDownloader.py
+++ b/youtube_dl/FileDownloader.py
@@ -121,7 +121,7 @@ class FileDownloader(object):
             exponent = 0
         else:
             exponent = int(math.log(bytes, 1024.0))
-        suffix = 'bkMGTPEZY'[exponent]
+        suffix = ['B','KiB','MiB','GiB','TiB','PiB','EiB','ZiB','YiB'][exponent]
         converted = float(bytes) / float(1024 ** exponent)
         return '%.2f%s' % (converted, suffix)