diff --git a/requirements.txt b/requirements.txt
index 51c0fb3..742156f 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -9,7 +9,7 @@ kiwisolver==1.0.1
 matplotlib==2.2.3
 mock==2.0.0
 networkx==2.2
-nltk==3.3
+nltk==3.6.3
 numpy==1.15.4
 pbr==5.1.0
 Pillow==5.3.0