diff --git a/requirements.txt b/requirements.txt
index d331002..067fdf3 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -6,7 +6,7 @@ pandas==1.2.4
 bcubed==1.5
 pyclustering==0.10.1.2
 matplotlib==3.3.4
-nltk==3.6.6
+nltk==3.9
 joblib==1.2.0
 gap-stat==2.0.1
 langdetect==1.0.8