diff --git a/wetb/fast/fast_io.py b/wetb/fast/fast_io.py
index 706420b1ef5152977a7496d5c7c69d2eea1439f6..619a789791d94c969a134c08f546b6bb69589bea 100644
--- a/wetb/fast/fast_io.py
+++ b/wetb/fast/fast_io.py
@@ -10,6 +10,7 @@ from __future__ import absolute_import
 from io import open
 from builtins import map
 from builtins import range
+from builtins import chr
 from future import standard_library
 standard_library.install_aliases()
 import os