diff --git a/requirements.txt b/requirements.txt
index 2cf9407..aca41c7 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -9,7 +9,7 @@ Markdown==3.3.3
 MarkupSafe==1.1.1
 mkdocs==1.1.2
 mkdocs-material==4.6.3
-nltk==3.5
+nltk==3.6.6
 Pygments==2.7.3
 pymdown-extensions==8.1
 PyYAML==5.3.1