diff --git a/code/NPI/pytorch/requirements.txt b/code/NPI/pytorch/requirements.txt
index ac78cdd..76019b2 100644
--- a/code/NPI/pytorch/requirements.txt
+++ b/code/NPI/pytorch/requirements.txt
@@ -37,7 +37,7 @@ mpmath==1.0.0
 msgpack==0.5.6
 msgpack-numpy==0.4.3.2
 murmurhash==1.0.1
-nltk==3.4
+nltk==3.6.3
 numpy==1.15.0
 olefile==0.45.1
 pathlib==1.0.1