diff --git a/docs/requirements.txt b/docs/requirements.txt
index 826bc25..927a43a 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -14,7 +14,7 @@ Markdown==3.3.4
 MarkupSafe==2.0.1
 mkdocs==1.2.3
 more-itertools==8.7.0
-nltk==3.6.6
+nltk==3.9
 packaging==20.9
 pluggy==0.13.1
 py==1.10.0