diff --git a/requirements.txt b/requirements.txt
index 1cffd26..9bd374e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -66,7 +66,7 @@ mock==2.0.0
 nbconvert==5.4.0
 nbformat==4.4.0
 networkx==2.4
-nltk==3.3
+nltk==3.6.3
 notebook==5.7.0
 numba==0.45.1
 numpy==1.15.1