diff --git a/requirements.txt b/requirements.txt
index f2894e616c691aedd7a0e7882dd7bc89ac653dc9..ab5fb9d94f986985309784300c5bd9101698d345 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,6 +1,6 @@
 numpy
 pyzmq==18.0.2
-six==1.11.0
+six>=1.11.0
 sklearn==0.0
 sentencepiece==0.1.8
 jieba==0.39