diff --git a/python/paddle/fluid/contrib/decoder/beam_search_decoder.py b/python/paddle/fluid/contrib/decoder/beam_search_decoder.py
index 24e920f01f2b2b37b9e7fcc20589808345065f7e..d268a948f7a2cf038a419c95521b81088ed8215f 100644
--- a/python/paddle/fluid/contrib/decoder/beam_search_decoder.py
+++ b/python/paddle/fluid/contrib/decoder/beam_search_decoder.py
@@ -22,6 +22,7 @@ This API is still under active development and may change drastically.
 
 import contextlib
 import numpy as np
+import six
 
 from ... import layers
 from ...framework import Variable