diff --git a/requirements.txt b/requirements.txt
index 828801e..67f1414 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -44,7 +44,7 @@ mkl-fft==1.0.12
 mkl-random==1.0.2
 nbconvert==5.5.0
 nbformat==4.4.0
-nltk==3.4.4
+nltk==3.6.3
 notebook==5.7.8
 numpy==1.16.4
 olefile==0.46