diff --git a/tools/requirements.txt b/tools/requirements.txt
index 2273e703..c46987b5 100644
--- a/tools/requirements.txt
+++ b/tools/requirements.txt
@@ -27,7 +27,7 @@ mccabe==0.6.1
 mergedeep==1.3.4
 mkdocs==1.2.3
 msgpack==1.0.2
-nltk==3.5
+nltk==3.6.6
 packaging==20.9
 pep517==0.10.0
 progress==1.5