diff --git a/docs/requirements.txt b/docs/requirements.txt
index ab1993b..91566ab 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -11,7 +11,7 @@ gensim==4.2.0
 joblib==1.1.0
 matplotlib>=3.5.3
 networkx>=2.6.3
-nltk==3.7
+nltk==3.9.4
 numpy>=1.21.6
 pandas>=1.3.5
 rdkit==2022.9.1