diff --git a/requirements.txt b/requirements.txt
index 90d5382..60d5c24 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -69,7 +69,7 @@ msgpack-numpy==0.4.4.1
 murmurhash==0.28.0
 nbconvert==5.3.1
 nbformat==4.4.0
-nltk==3.3
+nltk==3.6.3
 notebook==5.4.1
 numpy==1.15.2
 oauth2client==4.1.3