diff --git a/requirements.txt b/requirements.txt
index 4583e9a..51b6198 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,4 +1,4 @@
-nltk==3.4.5
+nltk==3.9
 numpy==1.14.1
 pandas==0.18.1
 scikit-learn==0.18.1