diff --git a/requirements.txt b/requirements.txt
index 064e5d0..85f291a 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -5,7 +5,7 @@ tensorflow==2.1.0
 pandas==0.25.3
 bert-for-tf2==0.13.5
 transformers==2.11.0
-nltk==3.5
+nltk==3.6.6
 tensorflow-hub==0.8.0
 sentencepiece==0.1.91
 joblib==0.16.0