diff --git a/requirements.txt b/requirements.txt
index 65f1ae5..cc1f99e 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -60,7 +60,7 @@ multipledispatch==0.4.8
 nbconvert==4.0.0
 nbformat==4.0.1
 networkx==1.10
-nltk==3.1
+nltk==3.4.5
 nose==1.3.7
 notebook==4.0.6
 numba==0.22.1