diff --git a/attention-tutorial/requirements.txt b/attention-tutorial/requirements.txt
index 010c5f23..ca30c6aa 100644
--- a/attention-tutorial/requirements.txt
+++ b/attention-tutorial/requirements.txt
@@ -29,7 +29,7 @@ MarkupSafe==1.0
 mistune==2.0.3
 nbconvert==6.5.1
 nbformat==4.4.0
-nltk==3.6.6
+nltk==3.9
 notebook==6.4.12
 numpy==1.22.0
 pandas==0.22.0