diff --git a/requirements.txt b/requirements.txt
index efc0ebd..868d73d 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -10,7 +10,7 @@ MarkupSafe==1.1.1
 mkdocs==1.1.2
 mkdocs-material==5.2.3
 mkdocs-material-extensions==1.0
-nltk==3.5
+nltk==3.6.6
 Pygments==2.6.1
 pymdown-extensions==7.1
 PyYAML==5.3.1