diff --git a/IRNet_deploy/requirements.txt b/IRNet_deploy/requirements.txt
index af0bd1f..5fb0f90 100644
--- a/IRNet_deploy/requirements.txt
+++ b/IRNet_deploy/requirements.txt
@@ -1,7 +1,7 @@
 # Copyright (c) Microsoft Corporation.
 # Licensed under the MIT license.
 
-nltk==3.4
+nltk==3.4.5
 pattern
 numpy==1.14.0
 pytorch-pretrained-bert==0.5.1