diff --git a/requirements.txt b/requirements.txt
index 4abdbcb..e6dbbb0 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -69,7 +69,7 @@ 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==0.21.0