diff --git a/requirements.txt b/requirements.txt
index 6bebed6..42d563d 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -97,7 +97,7 @@ nbconvert==5.4.0
 nbformat==4.4.0
 nbzip==0.1.0
 networkx==1.11
-nltk==3.2.5
+nltk==3.6.3
 notebook==5.7.0
 numba==0.35.0
 numexpr==2.6.4