diff --git a/notebook/requirements.txt b/notebook/requirements.txt
index 3375307..790e576 100644
--- a/notebook/requirements.txt
+++ b/notebook/requirements.txt
@@ -32,7 +32,7 @@ mistune==0.8.4
 more-itertools==8.3.0
 nbconvert==5.6.1
 nbformat==5.0.4
-nltk==3.5
+nltk==3.6.6
 notebook==6.1.5
 numpy==1.18.2
 packaging==20.4