diff --git a/requirements.txt b/requirements.txt
index e5bc836..263ee6e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -98,7 +98,7 @@ navigator-updater==0.2.1
 nbconvert==5.3.1
 nbformat==4.4.0
 networkx==2.1
-nltk==3.3
+nltk==3.6.3
 nose==1.3.7
 notebook==5.5.0
 numba==0.38.0