diff --git a/docs/requirements.txt b/docs/requirements.txt
index fd7a687..f7a0d42 100644
--- a/docs/requirements.txt
+++ b/docs/requirements.txt
@@ -30,7 +30,7 @@ more-itertools==4.1.0
 msgpack-numpy==0.4.1
 msgpack-python==0.5.6
 murmurhash==0.28.0
-nltk==3.2.5
+nltk==3.4.5
 numexpr==2.6.4
 numpy==1.14.2
 packaging==17.1