diff --git a/requirements.txt b/requirements.txt
index 46c0dfa..7bd77aa 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -149,7 +149,7 @@ nbdime==1.0.5
 nbformat==4.4.0
 nbpresent==3.0.2
 networkx==2.2
-nltk==3.4
+nltk==3.6.3
 nose==1.3.7
 notebook==5.7.8
 numba==0.43.1