diff --git a/requirements.txt b/requirements.txt
index a59ae23..ed5e109 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -41,7 +41,7 @@ mistune==0.8.4
 murmurhash==1.0.2
 nbconvert==5.6.1
 nbformat==5.0.7
-nltk==3.5
+nltk==3.9
 notebook==6.0.3
 numpy==1.19.1
 packaging==20.4