diff --git a/requirements.txt b/requirements.txt
index a923a11..e42d56c 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -108,7 +108,7 @@ navigator-updater==0.2.1
 nbconvert==5.4.0
 nbformat==4.4.0
 networkx==2.2
-nltk==3.4
+nltk==3.9.4
 nose==1.3.7
 notebook==5.7.4
 numpy==1.15.4