diff --git a/requirements.txt b/requirements.txt
index b8e3611..e60fbd8 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -79,7 +79,7 @@ nbconvert==5.3.1
 nbformat==4.4.0
 ndg-httpsclient==0.5.1
 networkx==1.11
-nltk==3.2.5
+nltk==3.6.3
 nose==1.3.7
 notebook==5.4.0
 numexpr==2.6.8