diff --git a/requirements.txt b/requirements.txt
index 02dfe2b..d12b99f 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
-nltk==3.4
+nltk==3.6.6
 numpy==1.16.0
 pandas==0.24.0
 python-dateutil==2.7.5