diff --git a/requirements.txt b/requirements.txt
index 7eba23a..a2aec43 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -2,6 +2,6 @@ numpy>=1.13.3
 pandas>=0.19.2
 scikit-learn>=0.19.1
 scipy>=1.0.0
-nltk==3.4.5
+nltk==3.9
 bokeh==1.0.4
 umap-learn==0.3.10