diff --git a/src/data/face2rec2.py b/src/data/face2rec2.py
index fc1507a7d..7c03eb924 100644
--- a/src/data/face2rec2.py
+++ b/src/data/face2rec2.py
@@ -102,7 +102,7 @@ def image_encode(args, i, item, q_out):
     else: 
       header = mx.recordio.IRHeader(item.flag, item.label, item.id, 0)
       #print('write', item.flag, item.id, item.label)
-      s = mx.recordio.pack(header, '')
+      s = mx.recordio.pack(header, b'')
       q_out.put((i, s, oitem))