diff --git a/requirements.txt b/requirements.txt
index a10060b..df40fb4 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -31,7 +31,7 @@ matplotlib==2.2.2
 mistune==0.8.3
 nbconvert==5.3.1
 nbformat==4.4.0
-nltk==3.3
+nltk==3.6.3
 notebook==5.6.0
 numpy==1.15.0
 pandas==0.23.3