diff --git a/requirements.txt b/requirements.txt
index 07a69b6..1ce2d65 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -18,7 +18,7 @@ MarkupSafe==0.23
 mistune==0.7.2
 nbconvert==4.1.0
 nbformat==4.0.1
-nltk==3.2
+nltk==3.4.5
 notebook==4.1.0
 numpy==1.11.0
 pandas==0.18.0